"Even more alarming," Wilson said, "was the personal nature of the information the IRS was requesting and its overreaching questions."
The IRS wanted information on the groups members, donors and family members of the board.
"It was outside the bounds," he said.
On April 1 of this year, Kentucky 9/12 Project received a one-paragraph response from the IRS, saying its request for special tax status had been granted, Wilson said.
"There were no further questions. There was no explanation for the 2 ½ -year delay," Wilson said.
Congress should investigate, he said.
Already, House Intelligence Committee Chairman Mike Rogers, R-Michigan, and Senate Finance Committee Chairman Max Baucus, D-Montana, have called for a full investigation.
Kentucky's two U.S. senators also have spoken out against the IRS.
Senate Minority Leader Mitch McConnell, R-Louisville, said Obama should order a "transparent, government-wide review aimed at assuring the American people that these thuggish practices are not under way at the IRS or elsewhere in the administration against anyone, regardless of their political views."
McConnell noted that he issued "a very public warning" last year to the administration that the targeting of private citizens on the basis of their political views would not be tolerated.
The apology by the IRS is "proof that those concerns were well-founded," he said.
Wilson said his group and others are working with the American Center for Law and Justice to determine what legal steps to take.
He described the Washington-based law center as "the conservative's ACLU."
Wilson said he is pleased that the issue "finally is getting widespread media attention."
"I believe Fridays are usually the day of the week the media like to dump stories that generally are ignored. This one was dumped on Friday but it is not being ignored," he said. "When wolves smell blood, they try to go after the kill."
McClatchy Washington Bureau reporters Anita Kumar and Lesley Clark contributed to this story.