CHICAGO (CBS) — The Chicago Teachers Union has joined a chorus of voices calling for Mayor Rahm Emanuel and Cook County State’s Attorney Anita Alvarez to resign over the Laquan McDonald police shooting scandal.

The union’s House of Delegates voted Wednesday night to approve a resolution demanding Emanuel and Alvarez “resign immediately from public office for the unconscionable delay of their governmental institutions in addressing Laquan McDonald’s killing and other issues of excessive, unwarranted, unjustified, and lethal police force in the City of Chicago that have surfaced in the aftermath.”

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The union and the mayor have been at loggerheads since his first term, leading to a teachers strike that lasted seven days at the start of the school year in 2012. The union is threatening to strike this year as well.

The resolution criticizes the mayor for fighting for more than a year to keep police dashboard camera video of McDonald’s death out of the public eye. Officer Jason Van Dyke shot McDonald 16 times in October 2014, after responding to calls about a person slashing tires.

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Police initially said McDonald lunged at officers with a knife, but the video shows McDonald walking away from police when Van Dyke shot him. Alvarez took more than a year to bring murder charges against Van Dyke, and did so only days after a Cook County judge ruled the city must release the video of the shooting. She filed charges just hours before Emanuel released the video.

“Both Cook County State’s Attorney Anita Alvarez and Mayor Rahm Emanuel orchestrated and intentionally delayed the release of these videos apparently for their own political gains in order to secure victory in their 2015 re-election bids,” the CTU resolution states. “The actions of both Mayor Rahm Emanuel and Cook County State’s Attorney Anita Alvarez impeded the criminal justice system, and in the process has led to the erosion of public trust and confidence in their leadership; and the only way to restore this trust is with their resignations.”

The resolution also blasts Emanuel’s maneuver to close half of the city’s mental health clinics in 2012, his decision to close 50 schools in 2013, and other cuts in services and staffing at public schools.

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Many activists and protesters have repeatedly called for Emanuel and Alvarez to resign over their handling of the McDonald case, but both have said they will not step down. Alvarez is up for re-election this year, and faces two challengers in the Democratic primary. Emanuel is not up for re-election until 2019.