(CNN) - Republicans opposed to Jack Lew's nomination to be treasury secretary may have a new line of criticism against him.
It's one which has been public for several years, but until recently received little scrutiny.
Multiple reports say an investment listed on 2009 financial disclosure paperwork when Lew was nominated to serve as a deputy secretary in the State Department is a fund based in the Cayman Islands.
The fund is CVCI Growth Partnership, described on the form as an employee investment fund. Prior to his State Department stint, Lew was employed at Citigroup as the chief operating officer of a business unit. A source familiar with the investments told CNN, "The fund was fully transparent for U.S. tax purposes - all income, gains, losses and expenses were reported on each investor's tax returns."
Lew invested $56,000 and sold his investment in 2010 for $54,418 when he was confirmed to lead President Barack Obama's budget office, the source said.
Obama was highly critical of GOP presidential nominee Mitt Romney for similar investments in funds based in the Cayman Islands.
Documents obtained by CNN show that Hank Paulson, a Treasury secretary under President George W. Bush, also declared Cayman Island accounts on financial disclosure forms.
Sen. Chuck Grassley, a Republican from Iowa and member of the Senate Finance Committee, blasted Lew over the investment.
"President Obama has been almost obsessively critical of offshore investments. He called Ugland House 'either the biggest building or the biggest tax scam on record,'" Grassley wrote in a statement late Friday.
Ugland House is a building in the Cayman Islands, which is the legal address for thousands of investment funds and businesses; the islands themselves are known as a tax haven for U.S. investors and companies. Obama mentioned Ugland House in the 2009 address Grassley cited, saying it "had over 12,000 business claim this building as their headquarters."
"For years, we've talked about shutting down overseas tax havens that let companies set up operations to avoid paying taxes in America," Obama said. He said his budget proposal would crack down on businesses which incorporate in places such as Ugland House.
Grassley said of the contrast between Obama's statements and Lew's past investment, "The irony is thick.
"On the White House claim that Mr. Lew previously disclosed his Ugland House investment, it was disclosed only if you knew where to look and then were able to put the pieces together. To say this information was fully disclosed to the public is misleading, at best," he charged.
White House spokesman Eric Schultz told CNN, "Jack Lew paid all of his taxes and reported all of the income, gains and losses from the investment on his tax returns. The existence of Mr. Lew's investment is not news to the Senate."
"There are no new facts that provide a basis for Senators to reach a different conclusion about Mr. Lew's nomination than they reached twice before in this Administration," he said.
Before Grassley's statement on Friday, Republicans two most significant concerns regarding Lew involved his work at Citigroup and his handling of Medicare when director of the White House Office of Management and Budget.
Before returning to government, he oversaw a Citigroup unit which made bets against the housing market ahead of that sector's collapse, which drove the 2008 financial crisis. Lew has said he did not make investment decisions for the group.
On Monday, a group of Republican senators claimed that when director of the White House Office of Management and Budget, Lew and the Obama administration fell short of requirements to report areas for policy change under a Medicare law.
The law requires the White House to submit legislation when Medicare trustees notice cash flow problems within the program. The White House has said previously it considers the particular law Republicans cited "to be advisory and not binding."
Lew stepped down as Obama's chief of staff late last month after being nominated for the top treasury spot.
His confirmation hearings have been scheduled for Wednesday.
Lew has been confirmed by the Senate for previous positions in both the Clinton and Obama administrations, but his current nomination receives a far greater level of scrutiny.
- CNN's Ted Barrett, Jennifer Liberto, Steve Brusk and Gregory Wallace contributed to this report