The powerful Chicago Teachers Union isn’t backing down from its endorsement of Cook County Board President Toni Preckwinkle for Chicago mayor — despite allegations that Ald. Ed Burke tried to extort a $10,000 campaign contribution from fast-food executives on her behalf.

On Wednesday, a federal criminal complaint charged Burke with one count of attempted extortion, alleging that he held up driveway and remodeling permits for a Burger King in a plot to steer real estate tax work to his law firm. The charges followed a federal probe that also uncovered the context surrounding the Preckwinkle contribution, which came in 2017 during her most recent campaign for county president.

“We aren’t going to get distracted by the politics of the day,” said union President Stacy Davis Gates. “The first black woman who can become the mayor of this city is the front-runner, and so as the front-runner her political opponents are taking the opportunity to draw connections that don’t exist in the way they think.”

Related: Chicago’s mayoral hopefuls are starting to release education plans. Here’s what we know so far.

With such a crowded field and no clear-cut leader in the race, it’s debatable whether Preckwinkle is the front-runner or not. But she is one of the most visible candidates running for mayor and a leader of Illinois’ Democratic Party. It remains to be seen how the Burke contribution will affect her chances.

Preckwinkle said in a statement Thursday that the contribution was tied to a 2017 fundraiser for her county board campaign hosted by Burke and Gery Chico, who volunteered and were “solely responsible for organizing and fundraising of this event.” She maintained that someone attempted to contribute via her website but the money wasn’t accepted, and insisted that her staff followed protocol.

But opponents like Illinois Comptroller Susana Mendoza and former schools chief Paul Vallas have blasted Preckwinkle for ties to the wealthy and powerful Burke, the longest-tenured alderman in Chicago history, whose wife sits on the state Supreme Court, and questioned her explanation.

Gates stressed that other candidates have ties to the longtime alderman too, including Chico, whom Burke endorsed for mayor, and Mendoza, who has called him her political mentor. Gates said, “There are mayoral contenders who owe their political careers to Burke, and President Preckwinkle is not one of them.”

The union pointed to several reasons for standing by Preckwinkle, including her support for a fully elected school board, an issue many candidates differ on; her pledge to freeze charter school expansion and school privatization; her opposition to school closings; and Preckwinkle’s emphasis on investing in social workers, school nurses and other support staff to provide wraparound services at neighborhood schools.

Related: On returning school control to voters, Chicago mayor candidates are split

“She stands by our struggle for the schools our students deserve, just as we stand by her mayoral bid,” Gates said.

On Friday, Burke stepped down from his post as chairman of the City Hall Finance Committee. As of 5 p.m. Friday, he hadn’t resigned from City Hall altogether as many critics have called for.