Assemblywoman Shelley Mayer picked up her first union endorsement this week in her bid to replace Westchester County-elect George Latimer in the state Senate.

Mayer was endorsed by TWU Local 100 in what is considered a key Senate race likely this spring.

“Working people have a champion in Shelley Mayer. She’s been with our school bus drivers and monitors 100% in their fight for earned sick time in Westchester. She’s a staunch supporter of grievance rights. She also stood by us in our contract fight at First Mile Square. She has the wholehearted support of Transport Workers Union Local 100,” said TWU Local 100 President Tony Utano.

Mayer is seeking the Democratic nod from local Party officials alongside Yonkers Mayor Mike Spano, Bedford Supervisor Chris Burdick and People for Bernie co-founder Kat Brezler.

The race is key to the push to reunify Democratic factions in the state Senate, based on a plan backed by Gov. Andrew Cuomo.