Casino mogul Steve Wynn resigned on Saturday as finance chairman of the Republican National Committee amid allegations of sexual harassment and assault.
Mr Wynn has been a prolific Republican donor and led the RNC's fundraising efforts during US President Donald Trump's first year, helping the committee rake in more than $130 million.
"Today I accepted Steve Wynn's resignation as Republican National Committee finance chair," said RNC chairwoman Ronna McDaniel.
The Wall Street Journal reported on Friday that a number of women said they were harassed or assaulted by Mr Wynn, the chairman and chief executive of Wynn Resorts. Mr Wynn has denied the allegations. One case led to a $7.5m settlement with a manicurist, the newspaper reported.
Mr Wynn was chosen by Mr Trump to lead the RNC's fundraising effort, and he contributed more than $600,000 to GOP causes last year, according to the Federal Election Commission.
A person with direct knowledge of the situation said Mr Trump had signed off on the decision for Mr Wynn to resign.
Since 2013, Mr Wynn has contributed nearly $2.4m to GOP candidates and party organisations around the country, including 2017 special election winners as well as dozens of state Republican Party committees.
The allegations against Mr Wynn have come during a wave of sexual misconduct claims against prominent media, entertainment and political figures that gained momentum last fall after the emergence of detailed allegations of rape and harassment involving movie producer Harvey Weinstein.
During the fall, RNC officials, including Ms McDaniel, noted that Mr Weinstein had been a top donor for Democrats, including 2016 presidential nominee Hillary Clinton.
In early October, Ms McDaniel tweeted that if the Democratic National Committee "truly stands up for women like they say they do, then returning Mr Weinstein's dirty money should be a no-brainer".
The RNC has not yet said whether it will return any money donated by Mr Wynn.
Mr Wynn was among the organisers of Mr Trump's fundraiser last week at his Mar-a-Lago resort in Florida to celebrate the anniversary of the inauguration. Mr Trump was unable to attend because of the federal government shutdown. Mr Wynn also helped put together high-dollar events in Dallas last October and New York City in December.
Mr Trump, addressing Nevada supporters in February 2016, praised Mr Wynn as a "great friend of mine".
"Steve is always calling. He's always got advice. Right, Steve? 'Donald, I think you ought to do this and that,'" Mr Trump said at the time. "His advice, I like to listen to, I'll be honest with you."
Members of the RNC are gathering in Washington next week and are expected to approve a new finance chair. The next chair will be voted on after the recommendation of Mr Trump and Ms McDaniel.