Teachers at a KIPP charter school in Brooklyn are moving forward with their campaign to form a union, undeterred by what they describe as managers’ moves to intimidate them. Indeed, rather than back down, the teachers leading the union drive have actually added one more person to their ranks.

Sixteen teachers filed petitions today to the state Public Employee Relations Board saying they want to unionize, working with the powerful United Federation of Teachers. That number is up from 15 teachers who were part of the original campaign last month. The first effort could have ended smoothly, with the teachers forming an official union, had leaders at KIPP recognized the effort within 30 days. But KIPP leaders did not recognize the campaign, leaving the state to judge whether the union should be formed.

The UFT in the last 10 days has filed two complaints to PERB on behalf of the teachers, accusing KIPP leaders of waging an intimidation campaign to stop staff from unionizing. A complaint filed this week accused KIPP co-founder David Levin of telling teachers that unionizing could throw teachers’ retirement benefits and pension plans “in jeopardy.” The complaint quoted Levin as saying “all of that goes away” if the teachers form a union.

Levin disputed that characterization in an interview this morning. “It wasn’t about discouraging them from doing that,” he said. “It was about providing them with information about what their rights and options are in this process.” He said he intends to cooperate with the law as the teachers work to form a union, and declined to say whether he plans to file counter-objections that could thwart the effort.

In a statement issued today, UFT President Randi Weingarten said KIPP has not cooperated with the union. “We are really disappointed that neither the initial thoughts expressed by management about working together nor the KIPP motto of team and family extend to the hardworking and dedicated teachers of the school,” Weingarten said.

The new petition to unionize has an additional difference from the one teachers sent to administrators last month: It lists the total number of teachers at KIPP AMP as 19, down from 20. A UFT spokesman, Brian Gibbons, said that apparently one teacher quit the school in the last month.