The revelations have prompted investigations by three congressional committees and the Justice Department. The inspector general, J. Russell George, is also continuing his review.
The agency's previous acting commissioner was forced to resign, another official retired and a third was placed on paid administrative leave.
A new inspector general's report, to be released Tuesday, says the IRS spent $50 million to hold at least 220 conferences for employees between 2010 and 2012.
The conference spending included $4 million for an August 2010 gathering in Anaheim, Calif., for which the agency did not negotiate lower room rates, even though that is standard government practice, according to a statement by the House Oversight and Government Reform Committee.
Instead, some of the 2,600 attendees received benefits, including baseball tickets and stays in presidential suites that normally cost $1,500 to $3,500 per night. In addition, 15 outside speakers were paid a total of $135,000 in fees, with one paid $17,000 to talk about "leadership through art," the committee said.
"I am absolutely appalled at the apparent waste of taxpayer dollars on frivolous conferences," said Rep. Harold Rogers, R-Ky., chairman of the full Appropriations Committee. "It seems we have a new misstep every day at the IRS."
Werfel has called the conference "an unfortunate vestige from a prior era."
White House spokesman Jay Carney said the president had not seen the forthcoming report dealing with IRS spending, but he also said Obama believes the IRS conduct was not appropriate.
"He is concerned by, and has been, excessive spending by the IRS and other agencies when it comes to conferences and travel, and has taken action accordingly," Carney said. "It's very important . . . that the American people have faith that the IRS, in particular, is applying our tax laws in a fair and responsible way."
Obama appointed Werfel as acting head of the IRS and ordered him to conduct a 30-day review of the agency's operations.
"Wherever we find management failures or breakdowns in internal controls, we will move to correct these problems quickly and in a robust manner," Werfel said. "As we move forward with our work, we will be transparent about what we learn, our specific plans for improvement, the actions we take and the results achieved."