Mr. Grimm also informed the House speaker, John A. Boehner, that he was stepping aside from his position on the Financial Services Committee. A spokesman for the speaker said Mr. Boehner believed that the move was “appropriate under the circumstances.”

The indictment creates potential problems for the Republican Party, which has backed Mr. Grimm, the only Republican in the New York City delegation, in his bid for a third congressional term this November against the Democratic challenger, Domenic M. Recchia Jr. The deadline to turn down his party’s nomination passed two weeks ago, meaning that Mr. Grimm is highly likely to stay on the ballot no matter what happens with the federal case.

Though the investigation, by the United States attorney’s office for the Eastern District of New York and the F.B.I., began by focusing on fund-raising, it took a turn midcourse to focus on the restaurant. Two fund-raisers on Mr. Grimm’s campaign have been charged: Diana Durand of Houston, who was accused of illegally giving more than $10,000 to his campaign, and Ofer Biton, who was being investigated to determine whether he had helped Mr. Grimm get around campaign-donation limits. Mr. Biton has pleaded guilty to visa fraud charges.

Mr. Biton and another man, Wayne Muratore, a certified public accountant from Brooklyn, were involved in both Mr. Grimm’s 2010 campaign and his restaurant business, providing a possible link that could have turned investigators from looking at the campaign to looking at Healthalicious. Mr. Muratore has not been charged.

Loretta E. Lynch, the United States attorney for the Eastern District of New York, did not detail why the investigation had changed. “Whenever there’s an investigation into someone’s business activities, it is usually very broad-reaching,” she said, adding that a larger investigation was continuing.

But, she said, Mr. Grimm had a sophisticated understanding of the law and finance, thanks in part to his background as an F.B.I. agent, where he did undercover work on Wall Street.