WASHINGTON (Reuters) - The White House’s budget chief came under fire on Thursday from Democrats and others over his attack on the budget research office of the U.S. Congress, escalating tensions between Republicans and professional staffers on Capitol Hill.

Office of Management and Budget Director Mick Mulvaney arrives at a Senate Budget Committee hearing on FY2018 Budget Proposals on Capitol Hill in Washington, U.S., May 25, 2017. REUTERS/Yuri Gripas

Office of Management and Budget Director Mick Mulvaney called “absurd” a recent finding by the nonpartisan Congressional Budget Office (CBO) that a Republican healthcare bill would cause 23 million people to lose health insurance coverage.

In an interview on Wednesday with the Washington Examiner, a conservative newspaper, Mulvaney said, “At some point, you’ve got to ask yourself, has the day of the CBO come and gone?”

Steny Hoyer, a Democratic House of Representatives leader, in a statement called Mulvaney’s comments “irresponsible and unacceptable” and an “indication of a bully mentality.”

The CBO is one of a handful of analysis units of Congress whose employees strive for political impartiality, providing dependable and neutral information that lawmakers can use when making often complex budget, tax and other decisions.

President Donald Trump and his fellow Republicans, including Mulvaney, have been frustrated with the CBO’s findings about their proposals to roll back Obamacare, the healthcare system put in place by then-Democratic President Barack Obama formally known as the Affordable Care Act.

“When Trump administration officials either disagree with or do not understand the impacts of their own policies, they prefer to attack the nonpartisan analysts who are doing their jobs with integrity and expertise,” Hoyer said in a statement.

Representative John Yarmuth, also a Democrat, said that Mulvaney had impugned the integrity of a CBO analyst in charge of the healthcare assessment and urged Mulvaney to apologize.

The CBO was created in 1974 during a spending dispute between the Democratic-controlled Congress and Republican President Richard Nixon after he withheld funds for government programs that did not support his political positions.

A CBO spokeswoman declined to comment on Thursday.

Former CBO Director Douglas Holtz-Eakin, a Republican who headed the office under President George W. Bush, said it was not unusual for the office to become a “political football.”

“What’s unusual here is to have the sitting OMB director attack the integrity, the core of the institution,” he said.

An OMB spokesperson could not be reached for comment.