A veteran Democratic state representative from Worcester resigned on Wednesday just as a House panel was poised to recommend that he be disciplined as part of an ethics investigation.

Representative John P. Fresolo, who was first elected to the Legislature in 1998, submitted a one-sentence letter to the House clerk saying he was “currently unable to effectively serve my district and regretfully submit my resignation,” effective immediately. He said he hoped that a special election would be scheduled to fill his seat.

Fresolo offered no details as to why he resigning and the secrecy surrounding the investigation continued Wednesday.

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A spokesman for House Speaker Robert A. DeLeo declined to comment on Fresolo’s departure, but said the speaker was in talks with Secretary of State William F. Galvin about the scheduling a special election.

Fresolo, 48, was under investigation by the House Ethics Committee, although the nature of the inquiry has not been made public, since the committee conducts its investigations in secret.

In the past, he has come under scrutiny for being one of the members who filed the greatest number of requests for per diem reimbursements, state payments that legislators are entitled to collect for commuting to and from the State House.

DeLeo’s office also said in March that a House employee had made allegations against a legislator, although the speaker declined to say if Fresolo was the lawmaker involved. Last month, the full House voted to give the Ethics Committee subpoena power to look into the matter.

An official briefed on the investigation told the Globe on Tuesday that the panel was poised to take action against Fresolo within days.

Fresolo, who served on the powerful House Ways and Means Committee, which oversees the $34 billion state budget, did not return phone messages on Wednesday.

In an interview with his local paper, the Worcester Telegram & Gazette, he said the House Ethics Committee had pressured him to resign.

“There was pressure to do this,” Fresolo told the paper. “I said that I was determined to fight, and I did try to fight as long as I could. It’s different now. I have been marginalized. I wouldn’t say I was treated fairly, but it’s a process, and I went through it and I am glad I did.”

Representative Bradley H. Jones Jr. the House Republican leader, said Wednesday that the Ethics Committee should forward any information or findings from its investigation to the appropriate authorities for further scrutiny.

“The necessary but overdue resignation of Representative Fresolo is an appropriate course of action given the circumstances,” Jones said in a statement. “The residents of the Sixteenth Worcester District and the taxpayers of Massachusetts deserve representatives and a governing body that is held to the highest ethical standard.”

Fresolo told the Telegram & Gazette that he was proud of his work as a state representative.

“I really cared a lot for the people I represented,” he said, adding, “I know in my heart I never did anything intentionally wrong.”