A leading labor group is launched a series of online advertisements Friday, seeking to thank Sen. Arlen Specter (D-Pa.) for tentatively backing "card check" legislation -- and hold him to that pledge.

American Rights at Work, a nonpartisan group backed by organized labor, set off an advertising campaign on Pennsylvania and national news websites building on Specter's pledge at a conference of liberal bloggers earlier this month that he would back cloture for a modified version of the Employee Free Choice Act (EFCA).

"I expect the cloture vote to occur on a modified version of the Employee's Free Choice legislation," Specter told the bloggers. "And I will support that cloture vote."

That position marked a reversal of Specter's previous stance, before he switched parties to seek reelection as a Democrat, when he pledged to not only oppose EFCA, but also any vote to end debate and bring it up for a final vote.

The American Rights at Work ad says Specter "listened" to that group in crafting his stance on the card check bill, a union organizing bill strongly supported by organized labor, and tells viewers to "thank Senator Specter and make sure he keeps listening."

The ad will run on national sites like the New York Times, Washington Post, and MSNBC websites, as well as several prominent political sites in Pennsylvania: Philly.com, PoliticsPA.com, KeystonePolitics.com, GrassrootsPA.com, and YoungPhillyPolitics.com.

View a sample of the ad below: