WASHINGTON (CNNMoney) -- Treasury Secretary nominee Jack Lew's first confirmation hearing got testy Wednesday as Republicans questioned his experience at Citigroup during the financial crisis.

In particular, lawmakers on the Senate Finance Committee asked Lew, now the White House Chief of Staff, about a fund organized in the Cayman Islands that he and other Citigroup employees invested in while he was employed there.

When asked if he was aware that the fund was in the Cayman Islands, Lew said he didn't know at the time.

"I was aware it was an international firm ... I didn't know at the time where the fund was organized," Lew said.

When he was confirmed as a Deputy Secretary of State in 2009, Lew declared that he had invested $56,000 in the fund. In 2010, during his confirmation hearing to be head of the Office of Management and Budget, Lew said he had divested from the fund, which had suffered a loss and he recovered $54,400.

The Obama administration has defended Lew's actions.

"Jack Lew paid all his taxes and reported all the income, gains and losses from the investment on his tax returns," White House spokesman Eric Schultz said.

In another area of contention, a group of eight Republican senators, including a few on the Finance Committee, sent a letter to the Office of Management and Budget last week saying that Lew didn't comply with a federal law over Medicare funds while he was running the White House budget office.

They say Lew, as White House budget chief, should have sent Congress legislation aimed at getting Medicare's funding in order, according to a federal law. But the White House counters that the law in question is advisory, not requisite.

In his prepared remarks, Lew, who was nominated last month to succeed Tim Geithner, stressed several times that his experience working on "almost every major bipartisan budget agreement over the last 30 years," is a big reason why the Senate should confirm him to the position.

"I can honestly say that the things that divide Washington right now are not as insurmountable as they might look," Lew said.

During the hearing, Lew was expected to make the case that Congress should stop the series of massive budget cuts, called a sequester, from taking place on March 1, slicing $85 billion from federal budgets.

"These cuts would impose self-inflicted wounds to the recovery and put far too many jobs and businesses at risk," Lew said in his prepared remarks.

-- CNN's Steve Brusk and Ted Barrett contributed to this report.