WASHINGTON — The Federal Election Commission said Thursday a conservative political group can use Republican-turned-Democrat Arlen Specter's campaign donor list to inform givers the senator has promised to return money to those upset by his switch.

The FCC voted 4-to-2 in favor of Club for Growth, a group once led by former Republican Rep. Pat Toomey. Toomey nearly defeated Specter in Pennsylvania's 2004 GOP primary and is running for the seat again.

The five-term Specter switched parties in April, in part to avoid facing Toomey a second time in the state's Republican primary. When Specter switched, he offered to return the money of any donors who asked for it back. His campaign has said he's given back about $225,000.

The FEC says the group can contact the donors, in part because it has promised not to solicit money.

Specter also faces a challenge by Rep. Joe Sestak in the state's Democratic primary.