Representative Nydia Velázquez and six other Democrats from Brooklyn will endorse a slate of three candidates in the New York City mayor’s race on Wednesday, hoping to stop former Gov. Andrew M. Cuomo’s momentum.

Ms. Velázquez, a progressive power broker who represents parts of Brooklyn and Queens, and her fellow Democrats will collectively back Adrienne Adams, the City Council speaker; Brad Lander, the city comptroller; and Zohran Mamdani, a state lawmaker from Queens.

Ms. Velázquez said in an interview that the city had been in chaos under Mayor Eric Adams and that New Yorkers deserved a leader with a “steady hand.” She said that Mr. Cuomo was leading in polls because people knew his name, but that voters deserved better choices who would stand up for working-class people.

“Brad and Adrienne and Zohran are all in this race for the right reasons,” she said. “They have integrity, decency and the desire to work with everyone to put the best interests of New Yorkers first.”

The endorsement shows how Democrats who oppose Mr. Cuomo are trying to coalesce around a few candidates in a crowded field ahead of the June 24 primary.

Ms. Velázquez will announce the endorsement with a group of allies from Brooklyn: Antonio Reynoso, the Brooklyn borough president; state lawmakers Julia Salazar and Emily Gallagher; and City Council members Jennifer Gutiérrez, Sandy Nurse and Lincoln Restler.