A new U.S. anti-tax evasion law, set to take effect on July 1, will encounter “inevitable glitches,” said the head of the U.S. Internal Revenue Service on Monday, adding that the IRS will be sympathetic to banks doing their best to comply.

The Foreign Account Tax Compliance Act (FATCA) will require foreign banks, insurers and investment funds to send the IRS information about Americans’ offshore accounts worth more than $50,000. Banks failing to comply could effectively be frozen out of U.S. capital markets.

FATCA’s start date has already been delayed twice. Some banking groups want another six-month delay, but the Obama administration has refused.

“We’ve held firm to the July 1 deadline because it’s already been extended,” IRS Commissioner John Koskinen said in a speech at a tax conference.

“The question is: How do we deal with the inevitable glitches along the way?” Koskinen said.

Acknowledging banks’ concerns about costs and complexity, he said, “We will be understanding of those problems as long as those (financial) intermediaries are making reasonable, good faith efforts to comply.”

Signed into law by President Barack Obama in 2010, the law was originally supposed to take effect on Jan. 1, 2013. That was postponed to Jan. 1, 2014, then to July 1 of this year.

(Editing by Kevin Drawbaugh, Bernard Orr)