Washington Teachers Union President Nathan Saunders will face challenger Elizabeth Davis in a runoff election for his seat, union officials said.

Saunders and Davis were among four candidates in the first round of voting, which ended last week. Saunders got 45 percent of the votes, and Davis got 41 percent.

Under union rules, a candidate must have more than 50 percent of the votes to win an election. Dates for the runoff election have not yet been set.

The race comes amid a flurry of education legislation that could have far-reaching implications for the teachers’ union, which already faces important questions due to the rise of nonunionized charter schools in recent years.

Mayor Vincent C. Gray (D) has introduced a bill that would give Schools Chancellor Kaya Henderson authority to approve new charters, potentially accelerating the shift away from unionized teachers. And D.C. Council Member David A. Catania (I-At Large) has introduced a legislative package that would transform some underperforming schools into “innovation schools” that would offer Henderson freedom from union rules.

Despite the pending legislation, turnout was low in the first round of union voting.

Of the 4,000 teachers working in the District’s school system, about 400 cast ballots, according to Davis and her supporters, who were present when votes were tallied June 7.

WTU officials declined to confirm that number, referring questions to the union’s elections committee. Cheryl Gillette, chairman of that committee, did not respond to requests for comment.

Saunders also declined to say how many teachers voted, but he acknowledged that “there could have been a better turnout in this race.”

Turnout could improve in the runoff election, Saunders said. After months of negotiating with school system officials over terms of a new collective-bargaining agreement, he plans to release details about that contract in coming days.

“We’re going to talk about it and I think it’s going to pique some interest,” Saunders said.

Davis has criticized Saunders for not speaking out more forcefully about recent D.C. public school administrators’ decisions to close 15 schools and to undergo “reconstitution” — in which all teachers must reapply for their jobs — at two others.

“He is so embedded with management at this point,” Davis said.

Saunders rejected that charge, saying that he has worked effectively to advocate for members, sometimes vocally and sometimes behind the scenes.

“Doing this job is not just about standing up and raising hell, it’s about actually getting something done that helps people at the end of the day,” Saunders said, arguing that he has worked to help teachers find jobs after being displaced by school closings and reconstitutions.