Representative Michael G. Grimm, a Republican from Staten Island who was easily re-elected to his third term in Congress last month despite a pending federal indictment, has agreed to plead guilty to a single felony charge of tax fraud, according to three people with knowledge of the matter.

A former Marine and agent with the Federal Bureau of Investigation who first ran for office as a law-and-order corruption fighter, Mr. Grimm, 44, is scheduled to appear in federal court in Brooklyn on Tuesday for a plea hearing, according to the docket sheet in his case, which provides no further detail. His trial was scheduled to start Feb. 2.

A guilty plea by the congressman, who has steadfastly maintained his innocence, would almost certainly put him under tremendous pressure to resign. One of his lawyers, Stuart N. Kaplan, said in an email that he could confirm only that there was “a change of plea hearing” scheduled for Tuesday.

Mr. Grimm was charged in a 20-count indictment in April after an investigation by federal prosecutors in Brooklyn, the Internal Revenue Service and the F.B.I. focused on accusations of campaign finance fraud and other improprieties. The indictment charged him with underreporting wages and revenue while he ran a fast-food restaurant called Healthalicious on the Upper East Side of Manhattan. He ran the business after the F.B.I. and before serving in Congress.