The New York State United Teachers has endorsed Suffolk County Water Authority Chairman Jim Gaughran's bid for the state Senate seat in northern Long Island currently held by Republican state Sen. Carl Marcellino.

On the surface, that's not terribly surprising. Gaughran is the Democrat running in one of the state's most competitive districts, and NYSUT is usually the top financial backer of Democrats running in competitive Senate seats.

But the endorsement is notable in that Marcellino is the chairman of his chamber's education committee. It's been at least a decade since the union has backed a challenger to a chair of the committee that handles the issues most important to teachers.

NYSUT stayed neutral in the race in 2016, when Marcellino wound up receiving only 50.6 percent of the vote against Gaughran.

But the union has feuded with Marcellino in recent months. He was the sponsor of a NYSUT-backed bill to overhaul the state's teacher evaluation system, which was never brought for a vote before the Senate.

"After every single Senate Republican and several Democrats turned their backs on New York teachers and public school students at the end of this year's legislative session, NYSUT vowed to remember who failed to stand with us," NYSUT President Andy Pallotta said in a statement.