A lawyer for the Goldwater Institute has sent letters to school superintendents across Arizona threatening to sue if they don't require striking teachers to return to work and re-open shuttered schools.
The letter sent Friday by the libertarian think tank tells school leaders that the strike is illegal and violates the state Constitution's requirement that students be guaranteed an education.
Attorney Timothy Sandefur's letter to superintendents says districts closed as part of "a coordinated plan to allow public school employees to refuse to report for duty or to discharge their contractual obligations."
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Schools districts enrolling the vast majority of the state's 1.1 million public school students were closed for a second day Friday as teachers rallied at the Capitol for more funding after years of cuts.
Photos: Massive #RedforEd march in Phoenix and Tucson in 2018
Arizona Teacher Walk Out
Updated
Apr 26, 2018
Approximately a thousand teachers, other staff and supporters line Congress Street at Granada Avenue on the first day of the statewide Arizona Teacher Walkout on April 26, 2018. Mamta Popat / Arizona Daily Star
Mamta Popat / Arizona Daily Star
Arizona Teacher Walk Out
Updated
Apr 26, 2018
Thousands march to the Arizona Capitol for higher teacher pay and school funding Thursday, April 26, 2018, in Phoenix. (AP Photo/Ross D. Franklin)
Ross D. Franklin
Arizona Teacher Walk Out
Updated
Apr 26, 2018
Approximately a thousand teachers, other staff and supporters line Congress Street at Granada Avenue on the first day of the statewide Arizona Teacher Walkout on April 26, 2018. Mamta Popat / Arizona Daily Star
Mamta Popat / Arizona Daily Star
Arizona Teacher Walk Out
Updated
Apr 26, 2018
"It's our day to be noticed," says Beatrice Goldsmith as she joined approximately a thousand teachers, other staff and supporters on Congress Street at Granada Avenue on the first day of the statewide Arizona Teacher Walkout on April 26, 2018. Mamta Popat / Arizona Daily Star
Mamta Popat / Arizona Daily Star
Arizona Teacher Walk Out
Updated
Apr 26, 2018
Teachers chant as they participate in a protest at the Arizona Capitol for higher teacher pay and school funding on the first day of a state-wide teachers strike Thursday, April 26, 2018, in Phoenix. (AP Photo/Ross D. Franklin)
Ross D. Franklin
Teacher Walk Out in Phoenix
Updated
Apr 26, 2018
Arizona teachers march to the Arizona State Capitol during a walkout for higher pay and more education funding on Apr. 26, 2018 in Phoenix, Ariz. (Photo by Rob Schumacher/The Arizona Republic)
Rob Schumacher / The Arizona Republic
Arizona Teacher Walk Out
Updated
Apr 30, 2018
Hundreds of Red For Ed supporters line Broadway Boulevard near Granada downtown during the teacher walkout on April 26, 2018, in Tucson, Ariz. Tucson participated in the statewide teacher walkout for the #RedForEd movement. Mike Christy / Arizona Daily Star
Mike Christy / Arizona Daily Star
Arizona Teacher Walk Out
Updated
Apr 27, 2018
Teachers march down Jefferson during the Arizona teacher walkout in Phoenix, Az., on April 26, 2018.
Cheryl Evans / The Arizona Republic
Arizona Teacher Walk Out
Updated
Apr 26, 2018
Motorists show their support for teachers and community members gathered downtown near Broadway and Granada during the teacher walkout on April 26, 2018, in Tucson, Ariz. Tucson participated in the statewide teacher walkout for the #RedForEd movement.
Mike Christy / Arizona Daily Star
Arizona Teacher Walk Out
Updated
Apr 30, 2018
Teachers and supporters hold their Red For Ed signage on the pedestrian bridge over Broadway Boulveard downtown during the teacher walkout on April 26, 2018, in Tucson, Ariz. Tucson participated in the statewide teacher walkout for the #RedForEd movement.
Mike Christy / Arizona Daily Star
Arizona Teacher Walk Out
Updated
Apr 26, 2018
Approximately a thousand teachers, other staff and supporters line Congress Street at Granada Avenue on the first day of the statewide Arizona Teacher Walkout on April 26, 2018.
Mamta Popat / Arizona Daily Star
Arizona Teacher Walk Out
Updated
Apr 26, 2018
Approximately a thousand teachers, other staff and supporters line Congress Street at Granada Avenue on the first day of the statewide Arizona Teacher Walkout on April 26, 2018.
Mamta Popat / Arizona Daily Star
Arizona Teacher Walk Out
Updated
Apr 26, 2018
Approximately a thousand teachers, other staff and supporters line Congress Street at Granada Avenue on the first day of the statewide Arizona Teacher Walkout on April 26, 2018. Supporters stand on the pedestrian bridge that crosses over Congress Street.
Mamta Popat / Arizona Daily Star
Arizona Teacher Walk Out
Updated
Apr 26, 2018
Approximately a thousand teachers, other staff and supporters line Congress Street at Granada Avenue on the first day of the statewide Arizona Teacher Walkout on April 26, 2018.
Mamta Popat / Arizona Daily Star
Arizona Teacher Walk Out
Updated
Apr 26, 2018
A man stands in the crosswalk on Congress Street near Granada Avenue on the first day of the statewide Arizona Teacher Walkout on April 26, 2018. Approximately a thousand people lined Congress Street to show their support for #Red4Ed.
Mamta Popat / Arizona Daily Star
Arizona Teacher Walk Out
Updated
Apr 26, 2018
Approximately a thousand teachers, other staff and supporters line Congress Street at Granada Avenue on the first day of the statewide Arizona Teacher Walkout on April 26, 2018.
Mamta Popat / Arizona Daily Star
Arizona Teacher Walk Out
Updated
Apr 26, 2018
Isaac Rivas, 11, right, pours water into his brother's, Ismael's, 11, mouth as the two take a break from protesting with their mom who's a teacher in the Catalina Foothills School District during the first day of a statewide Arizona Teacher Walkout on April 26, 2018. Approximately a thousand people lined Congress Street to show their support for #Red4Ed.
Mamta Popat / Arizona Daily Star
Arizona Teacher Walk Out
Updated
Apr 26, 2018
Thousands march to the Arizona Capitol for higher teacher pay and school funding Thursday, April 26, 2018, in Phoenix. (AP Photo/Ross D. Franklin)
Ross D. Franklin
Arizona Teacher Walk Out
Updated
Apr 26, 2018
Thousands march to the Arizona Capitol for higher teacher pay and school funding Thursday, April 26, 2018, in Phoenix. (AP Photo/Ross D. Franklin)
Ross D. Franklin
Arizona Teacher Walk Out
Updated
Apr 26, 2018
A protester chants along with thousands of others as they participate in a protest at the Arizona Capitol for higher teacher pay and school funding on the first day of a state-wide teachers strike Thursday, April 26, 2018, in Phoenix. (AP Photo/Ross D. Franklin)
Ross D. Franklin
Arizona Teacher Walk Out
Updated
Apr 26, 2018
Participants chant during a protest at the Arizona Capitol for higher teacher pay and school funding on the first day of a state-wide teachers strike Thursday, April 26, 2018, in Phoenix. (AP Photo/Ross D. Franklin)
Ross D. Franklin
Arizona Teacher Walk Out
Updated
Apr 26, 2018
Thousands march on the Arizona Capitol for higher teacher pay and school funding on the first day of a state-wide teachers strike Thursday, April 26, 2018, in Phoenix. A sea of teachers clad in red shirts and holding "Money for Schools" signs reached the Arizona Capitol to press lawmakers for action Thursday, a key event in an unprecedented walkout that closed most of the state's public schools and built on an educator uprising that bubbled up in other parts of the U.S. (AP Photo/Ross D. Franklin)
Ross D. Franklin
Arizona Teacher Walk Out
Updated
Apr 26, 2018
Thousands chant as they participate in a protest at the Arizona Capitol for higher teacher pay and school funding on the first day of a state-wide teachers strike Thursday, April 26, 2018, in Phoenix. (AP Photo/Ross D. Franklin)
Ross D. Franklin
Arizona Teacher Walk Out
Updated
Apr 26, 2018
Thousands participate in a protest at the Arizona Capitol for higher teacher pay and school funding on the first day of a state-wide teachers strike Thursday, April 26, 2018, in Phoenix. A sea of teachers clad in red shirts and holding "Money for Schools" signs reached the Arizona Capitol to press lawmakers for action Thursday, a key event in an unprecedented walkout that closed most of the state's public schools and built on an educator uprising that bubbled up in other parts of the U.S. (AP Photo/Ross D. Franklin)
Ross D. Franklin
Arizona Teacher Walk Out
Updated
Apr 26, 2018
Diana Tapia drops off her son Alec, 3, to the day care at Walker Early Learning Center on the campus of Walker Elementary School which is open during the teacher walkout on April 26, 2018 in Tucson, AZ. Tapia said she would take her daughter Anail, 7, left, a Walker Elementary student with her to work.
Ron Medvescek / Arizona Daily Star
Arizona Teacher Walk Out
Updated
Jul 8, 2018
Cayce Miners, an orchestra teacher at Tucson High Magnet School, writes #RedforEd on his car window before driving to Phoenix, Ariz. for a rally as part of the first day of the statewide Arizona Teacher Walkout on April 26, 2018. Photo by Mamta Popat / Arizona Daily Star
Mamta Popat / Arizona Daily Star
Arizona Teacher Walkout: Day One
Updated
May 1, 2018
Callista Radloff, a teacher from Safford K-8 School, speaks to a group of teachers, support staff and supporters at the Pima College Community West campus before driving to Phoenix, Ariz. for a rally as part of the first day of the statewide Arizona Teacher Walkout on April 26, 2018.
Mamta Popat / Arizona Daily Star
Arizona Teacher Walk Out
Updated
Apr 26, 2018
A maintenance staffer at Catalina Foothills High School north of Tucson, Ariz., moves tables in a dark, quiet classroom wing during the first day of the statewide Teacher Walk Out on April 26, 2018.
Rick Wiley / Arizona Daily Star
Arizona Teacher Walk Out
Updated
Apr 26, 2018
A dark, empty cafeteria at Catalina Foothills High School north of Tucson, Ariz., that can handle as much as 1,800 students during a normal school day is dark and quiet during the first day of the statewide Teacher Walk Out on April 26, 2018.
Rick Wiley / Arizona Daily Star
Arizona Teacher Walk Out
Updated
Apr 26, 2018
Six-year-old Liam Evans studies the bubbles from his bubble gun on the playground gym at Brandi Fenton Memorial Park during the teacher walkout on April 26, 2018 in Tucson, AZ. Liam was out enjoying his "day off" from the Khalsa School with his family.
Ron Medvescek / Arizona Daily Star
Arizona Teacher Walk Out
Updated
Apr 26, 2018
Destiny Valdez, left, a sixth-grader at Walter Douglas Elementary School, feeds younger brother Channing Stafford, 2, a grape at a lightly-attended lunchtime at the school, 3302 N. Flowing Wells Road, during the teacher walkout on April 26, 2018, in Tucson, Ariz. The school served 16 lunches on Thursday.
Mike Christy / Arizona Daily Star
Arizona Teacher Walk Out
Updated
Apr 26, 2018
Tucson Unified School District busses sit empty at the transportation center on the first day of the statewide Arizona Teacher Walkout on April 26, 2018.
Mamta Popat / Arizona Daily Star