Boston Teachers Union president Richard Stutman told WBUR he "can't imagine" that the union will endorse a mayoral candidate before the preliminary election Sept. 24, when voters will narrow the field from 12 to two.
At this late stage, he said, endorsing a candidate is simply not feasible.
But Stutman said the union may back a candidate before the final election Nov. 5.
The union, which is hosting a mayoral forum Wednesday night, is a potent force, representing 10,000 teachers, nurses, guidance counselors and retirees, among others.
Stutman said the union would be comfortable with "a number" of the candidates running for mayor. But he declined to name them.
City Councilor Felix Arroyo and state Rep. Martin Walsh both have union backgrounds, though Walsh has come out in favor of lifting the state's cap on charter schools, which is opposed by the BTU.
City Councilor Rob Consalvo has repeatedly spoken out against the "demonizing" of teachers. And City Councilor Mike Ross is opposed to lifting the charter school cap.
Stutman has publicly criticized City Councilor John Connolly, who is a full-throated supporter of an education reform movement that favors charter schools and greater management flexibility than the teachers contract offers.
Stand for Children, a national education reform advocacy group with a chapter in Massachusetts, threw its support behind Connolly last month with plans to spend more than $500,000 on an independent expenditure campaign on his behalf.
But Connolly told the group not to spend on his behalf amid an uproar over the role of outside money in the campaign.
The BTU forum, moderated by Boston Magazine and WGBH contributor David Bernstein, is scheduled for 7 pm at the union headquarters, 180 Mt. Vernon St., Dorchester.
Eleven candidates have confirmed for the event.
This program aired on September 11, 2013. The audio for this program is not available.