A union that represents thousands of Philadelphia city employees sued Mayor Cherelle L. Parker’s administration Tuesday over the mayor’s return-to-office policy, asking a judge to halt the mandate before it takes effect July 15.

The lawsuit was filed by District Council 47 of the American Federation of State, County and Municipal Employees, which represents 6,000 administrative and supervisory employees. The suit claims that the city violated its contract by requiring all employees to return to in-person work.

“The city’s 180-degree turn will cause substantial harm for city workers, and will throw city services into chaos,” the union wrote in its suit.

DC 47 also filed a companion unfair labor practices complaint with the Pennsylvania Labor Relations Board.