Sen. Susan Collins (R-Maine) on Sunday called the Internal Revenue Service's singling out of conservative groups for extra scrutiny "absolutely chilling" and called on President Obama to condemn the effort.

"This is truly outrageous and it contributes to the profound distrust that the American people have in government," Collins, a moderate Republican, said on CNN's "State of the Union." "It is absolutely chilling that the IRS was singling out conservative groups for extra review, and I think it's very disappointing that the president hasn't personally condemned this and spoken out."

The IRS apologized Friday for flagging groups seeking tax-exempt status with "tea party" or "patriot" in their names for extra attention. The official who oversees tax-exempt groups at the agency said the effort was not motivated by partisanship. White House Press Secretary Jay Carney said Obama was "concerned" about the reported behavior "of a small number" of IRS employees.