Senators examining the case of unwarranted scrutiny of conservative groups that sought tax exempt status will hear for the first time on Tuesday from the man who was in charge of the U.S. tax collection agency when it singled out the groups, one of three potentially damaging issues consuming the first months of President Barack Obama's second term.

Members of the Senate Finance Committee will be asking former Internal Revenue Service Commissioner Douglas Shulman what he knew about the conduct of his agency and when he knew it.

Beyond that will be why the IRS was paying special attention to conservative groups. Shulman was appointed head of the IRS by former President George W. Bush and didn't leave left the IRS until November when his five-year term ended.

Opposition Republicans have seized on the audit by a Treasury Department inspector general, which found that Internal Revenue Service employees singled out groups with names like ``tea party'' and ``patriots'' for special scrutiny that delayed their applications for tax exempt status -- including during last year's presidential election.

Conservative organizations critical of Obama and his fellow Democrats often refer to themselves as tea party or patriot groups.

Republicans are using the news to criticize Obama ahead of next year's elections for Congress.

The controversy also has reignited the small-government tea party movement, whose influence in last year's election had waned compared to its muscular role in 2010.

(AP)