Rep. Joe Sestak (D-Pa.) is a serious Senate candidate, Service Employees' International Union (SEIU) President Andy Stern tweeted Tuesday.

Stern had met with Sestak yesterday to discuss the Democrat's intentions in the Pennsylvania Senate race. Sestak has been making a lot of noise as of late about challenging Sen. Arlen Specter (D) in the state's 2010 Democratic primary.

Stern tweeted Tuesday morning:
Sestak is serious about Senate race. Doing Senate Finance Roundtable today on health care.

Beyond their traditional influence in Democratic contests, union leaders have made clear that their support for Specter in a primary is still an open question. Specter has said he opposes the Employee Free Choice Act (EFCA), a prized piece of union legislation, even after having switched parties to pursue reelection as a Democrat.

Cross-posted at the Briefing Room.