(CNN) - New radio ads will begin airing in three states as early as Sunday to help counter criticism of a handful of Republican senators who have said they will support President Obama's economic recovery plan.
The ads - paid for by the liberal interest group Americans United for Change - will "thank" Sens. Susan Collins and Olympia Snow of Maine and Sen. Arlen Specter of Pennsylvania. The ad also highlights Nebraska's Sen. Ben Nelson, a centrist Democrat in the middle of the negotiations over the $827 billion proposal.
All four lawmakers are considered key to getting the proposal approved in the Senate. The vote is expected to come early this week.
The ads ask listeners to call their senators to "thank them for their leadership and tell them to keep fighting for a plan to get our economy moving again."
"We want to acknowledge the work they contributed to getting a deal and encourage them to hold firm," Americans United President Brad Woodhouse told CNN.
The ad buy is likely to include the cities of Portland and Bangor in Maine; Omaha, Nebraska; and Philadelphia, Pennsylvania.