Martin Shkreli’s social-media habits have once again gotten him in serious trouble: A post of his about Hillary Clinton set off a Secret Service investigation and a request from federal prosecutors to revoke his bail because he poses “a risk of danger to the community.”

Prosecutors told the federal judge overseeing Mr. Shkreli’s case that they were concerned that his followers would “take his statements seriously — as has happened previously — and act on them.” Judge Kiyo A. Matsumoto scheduled a Sept. 14 hearing on the government’s motion, which, if upheld, would return Mr. Shkreli to jail.

Mr. Shkreli, 34, a pharmaceutical executive who gained infamy for his price increase for the lifesaving drug Daraprim, was convicted in August after a five-week federal trial on three of eight fraud counts related to hedge funds he ran.

He remains free on $5 million bail, as he has been since shortly after his arrest in 2015.

The prosecutors’ request involves a Facebook post of Mr. Shkreli’s from Monday. “On HRC’s book tour, try to grab a hair from her,” Mr. Shkreli wrote, referring to Mrs. Clinton, who has a book scheduled to come out next week. “Will pay $5,000 per hair obtained from Hillary Clinton.”