The Cambridge-born Red Sox fanatic went on YouTube to announce that if more than 200,000 New Yorkers vote for the Working Families Party, he'll don a Yankees cap in a new video.
"I'm serious," Damon says in his pitch. "Please tell your friends."
The actor also mentions that the pary is at the forefront of fighting against hydro-fracking, a controversial gas-drilling procedure.
WATCH Damon's plea in the video below: