US lawyer Michael Avenatti, who represented porn star Stormy Daniels in her lawsuit against President Trump, has been arrested on fraud charges.
Prosecutors says he tried to extort more than $20m (£15m) from Nike, threatening to use his profile to inflict reputational harm on the firm.
In a separate case, the 48-year-old has been accused of embezzlement.
A frequent guest on TV news and talk shows, Mr Avenatti emerged as a fierce critic of Donald Trump.
At one point he said he was considering running for president himself in 2010.
Mr Avenatti appeared in a New York court on Monday and was released on $300,000 (£227,000) bail on condition that he surrender his US and Italian passports. He did not enter a plea.
Outside court, he said he was confident he would be "fully exonerated".
He told reporters he had spent his career fighting powerful people and powerful corporations and that he would "never stop fighting that good fight".
What are the Nike charges about?
According to federal prosecutors in New York, Mr Avenatti met a lawyer for Nike earlier this month. During their meeting, he allegedly threatened to release damaging information about the company unless it paid him and another, unnamed co-conspirator between $15m (£11.4m) and $25m (£19m).
He also demanded $1.5m (£1.13m) for an individual he claimed to represent.
Mr Avenatti reportedly threatened to take $10bn (£7.56bn) off Nike's market value.
He was arrested in New York on Monday, shortly after announcing that he would hold a news conference about a scandal surrounding Nike on Tuesday.