The two unions that, put together, represent the vast majority of the city school system’s employees, took differing approaches to endorsing candidates of a tight Congressional primary race in Brooklyn this afternoon.

One of them, DC-37, which represents 25,000 Department of Education employees, endorsed Councilman Charles Barron in what some attributed to a not-so-subtle rejection of his opponent’s supportive position on charter schools. The other, the United Federation of Teachers, which represents 75,000 teachers and 200,000 members in total, just announced that it wouldn’t endorse anyone at all.

Neither union mentioned Barron’s opponent, Assemblyman Hakeem Jeffries, in their emailed statements. Jeffries is the favored candidate among his fellow elected officials and has already collected an endorsement from the city’s powerful Healthcare Workers Union.

Jeffries has been vocal on education issues in the past year and has not always seen eye-to-eye with the teachers union. Last summer, Jeffries and fellow Brooklyn Assemblyman Karim Camara wrote an op-ed explaining their opposition to a lawsuit against charter school co-locations that was brought but the UFT and NAACP. He later gave a more absolute endorsement of charter schools, the vast majority of which are staffed with non-union employees, he visited one in Bedford-Stuyvesant last year.

“Over the past year, city workers and their unions have had to fight major battles to protect rights that we fought hard to win as well as to preserve the vital safety-net services we provide to an ever-growing clientele,” said DC-37 Executive Director Lilian Roberts in a statement.

Barron, on the other hand, is one of the Council’s most staunch critics of charter schools. And when the education department laid off nearly 800 school aides, parent coordinators and paraprofessionals last year, Barron was among many Council members who protested the cuts.

The Congressional primary is scheduled for June 26, months earlier than usual, and is likely have a low voter turnout. Endorsements play a significant role in such elections because of unions’ abilities to mobilize its membership to the ballots.

When the UFT sat out of the 2009 mayoral race, Bill Thompson lost by less than 5 percentage points, leading to speculation that had the union supported Thompson, a Democrat, the outcome would have been different.