The senator and presidential candidate will join the city’s teachers, school support staff and other unions — including striking GM workers from Detroit — at Tuesday’s rally in Chicago.

In the midst of heated contract negotiations with Mayor Lori Lightfoot, the Chicago Teachers Union is getting a boost from a major supporter.

Democratic presidential hopeful and U.S. Sen. Bernie Sanders from Vermont is coming to Chicago Tuesday to join a 7 p.m. labor rally at CTU headquarters on the Near West Side.

Members of several other unions will be there, including support staff at Chicago Public Schools who are represented by Service Employees International Union Local 73. The more than 7,000 special education classroom assistants, bus aides, security guards and custodians with SEIU Local 73 have already authorized a potential mid-October work stoppage.

Striking General Motors workers with the United Automobile Workers union are also expected to be among those joining the group.

“Senator Sanders has been a stalwart supporter of union workers and their right to strike when necessary for dignity and decent wages and working conditions. He has also championed quality health care for all, a key issue in bargaining for both the CTU and SEIU Local 73,” the CTU said in a statement.

Sanders last week posted a message of support on Twitter for the city’s teachers: “I stand with the educators and support staff of [CTU] and [SEIU Local 73] in their fight for the schools Chicago’s students deserve. It’s unconscionable for wealthy corporations to receive massive tax breaks while children go without school nurses and librarians.”

CTU members are taking a strike authorization vote from Tuesday to Thursday. If it passes with at least 75% of the votes, the earliest a walkout could happen is Oct. 7. Both the CTU and Lightfoot have expressed interest in agreeing to a deal to avert a strike.

The city has offered both the CTU and SEIU a pay and benefits package that includes 16% raises over five years, and Lightfoot said Friday that she would be willing to sit at the CTU bargaining table herself to hammer out a deal.

But union leaders have said the contract is about more than just money, as the two sides remain in negotiations over teacher preparation time, class size and staffing shortages.