One of the largest unions in Massachusetts launched ads statewide on Thursday against Sen. Scott Brown (R), pressuring him to vote against the 2012 Republican budget in the Senate.

1999 SEIU, an affiliate of the Service Employees International Union representing healthcare workers on the East Coast, produced a minute-long radio ad hammering Brown over the Republican budget and its plan to reform Medicare.

The ads will run statewide until the Senate vote, expected next week, on the budget authored by Rep. Paul Ryan (R-Wis.) that passed the House earlier this year.

Republicans like Brown, who's expected to face a relatively tough reelection effort in a normally-Democratic state, have faced pressure from liberal groups over the vote.

Democrats have been quick to seize on a statement of support Brown made last week in which he suggested he'd support the budget, even though he expected it to fail in the Senate.

“We’re not asking Scott Brown to change his talking points on this dangerous plan to destroy Medicare,” a healthcare worker said in a release. “We’re asking Scott Brown to change his vote on this plan which would end Medicare as we know it and jeopardize the health of thousands of vulnerable seniors."

Since making his initial declaration of support, Brown's been more dodgy about his support for the Medicare reform provision in the budget — the central part of liberals' criticism.

Senate Majority Leader Harry Reid (D-Nev.) has signaled he'll bring up next week a vote on the budget in its entirety, precisely to put Republican senators like Brown on the spot. Listen to audio of the ad below: