Hours after announcing his switch to the majority party in the Senate, newly minted Pennsylvania Democrat Arlen Specter has already put his fundraising team (or his future, Democratic fundraising team) in a challenging position.

After revealing his decision, Specter promised to return recent campaign contributions to any donor “upon request.” With a war chest of more than $6.7 million in cash on hand as of the most recent filing period, he could be paying back millions. While Specter has received promises of fundraising help from Pennsylvania Gov. Ed Rendell and the national Democratic establishment, his promise may prove to be an expensive stand on principle.

Among the first in line to demand their money back may be more than a dozen current and former congressional colleagues who have donated more than $65,000 already to his 2010 re-election efforts.

Included in this list are such notables as Republican Minority Leader Mitch McConnell ($10,000 from his Bluegrass Committee PAC), Republican Conference Chair Lamar Alexander ($5,000 from his Tennessee PAC), Republican Senate legend Orrin Hatch ($10,000 from his ORRIN PAC), former Pennsylvania senatorial colleague Rick Santorum ($5,000 from his America’s Foundation PAC), and former Republican Majority Leader Bill Frist ($3,000 from his Volunteer PAC).

One leadership PAC that may expand its support for the newest member of the Democratic caucus? Specter’s own Big Tent PAC, which ended 2008 with $8,650 in cash.