He added, "This should send a chill up your spine. . . . I don't know where it stops or who is involved."
Congressional Republicans already are conducting several investigations and asked for more.
"This mea culpa is not an honest one," said Rep. Darrell Issa, R-Calif.
After the AP report Saturday, White House press secretary Jay Carney said that if the inspector general "finds that there were any rules broken or that conduct of government officials did not meet the standards required of them, the president expects that swift and appropriate steps will be taken to address any misconduct."
Collins said the revelations about the nation's tax agency only contribute to "the profound distrust that the American people have in government. It is absolutely chilling that the IRS was singling out conservative groups for extra review."
She said she was disappointed that Obama "hasn't personally condemned this." The president, Collins said, "needs to make crystal clear that this is totally unacceptable."
Lerner said that about 300 groups were singled out for additional review, with about one-quarter scrutinized because they had "tea party" or "patriot" somewhere in their applications.
Lerner said 150 of the cases have been closed and no group had its tax-exempt status revoked, though some withdrew their applications.
Collins appeared on CNN's "State of the Union," Rogers was on "Fox News Sunday" and Issa spoke on NBC's "Meet the Press."