CHICAGO (CBS) — Opening a new front in the ongoing contract dispute between Chicago Public Schools and the Chicago Teachers Union, Mayor Lori Lightfoot complained the union is holding up negotiations over demands on affordable housing policy.

In a statement Tuesday night, Lightfoot said that the union’s contract with CPS is “not the appropriate place for the city to legislate its affordable housing policy,” but CTU responded Wednesday morning that 17,000 students in the district are homeless.

“Yet Lori Lightfoot insists on mocking us instead of discussing the housing needs of those students and their families,” the union wrote in a Facebook post.

With only eight days until the union’s strike deadline, the mayor’s statement said rather than providing a comprehensive contract proposal she has demanded, “CTU presented its demands to set the city’s affordable housing policy through their collective bargaining agreement, demanding that the city enact CTU’s preferred affordable housing policy as part of their contract.”

Lightfoot said the city and CTU share many of the same priorities on affordable housing, and she welcomes teachers’ input on policy discussions, but said the teachers’ employment contract is not the place for such discussions.

“We are a week away from our deadline to resolve this contract and avoid a strike. We need CTU to come to the table with written proposals on the core issues we need to address in order to resolve the contract. Once this contract is resolved, our Department of Housing will continue to work closely with stakeholders—including unions like the CTU—to ensure everyone in all of our communities has access to a safe, affordable, accessible place to live,” the mayor said.

The union defended its positions on affordable housing Wednesday morning, noting there are approximately 17,000 homeless students at CPS.

“Our contract proposals demand CPS hire staff to support CPS families in danger of losing their housing, and advocate for a program that financially helps our PSRPs and new teachers purchase a home. The mayor finds them ‘unreasonable,'” the union stated in a Facebook post.

The union has said they want to negotiate on issues beyond teachers’ pay and health benefits — including class sizes; increased numbers of nurses, librarians, social workers, and counselors;