Michael Grimm Resists Calls for Resignation After Guilty Plea to Tax Charge

— -- After pleading guilty to a felony tax charge in federal court today, Rep. Michael Grimm made it clear he has no plans to resign from office despite mounting pressure from Democrats.

"No," Grimm told reporters outside the courtroom when asked if he would resign. "As I said before as long as I am able to serve I will serve."

Grimm pleaded guilty to a single count of aiding in the preparation of a false tax return in 2009 and also agreed to pay an undetermined amount of restitution to the IRS and New York State on tax returns dating from 2007 to 2010. Grimm faces a maximum sentence of three years in prison and is set to be sentenced on June 8 in arguably the highest-profile public corruption case in New York in decades.

Facing reporters after the hearing, Grimm owned up to making some "big mistakes,” explaining that he "underreported" sales receipts to pay business expenses, including compensating employees "off the books."

"As a result the taxes were inaccurate," Grimm admitted. "It's wrong...I should not have done it."

Grimm arrived in the courtroom shortly after 1 p.m. surrounded by a mob of photographers and reporters. A string of FBI agents including Rich Frankel, the head of the criminal division of the New York field office, lined the back row of spectators.

Asked by Judge Pamela K. Chen whether he understood the criminal charge that he was pleading guilty to, Grimm replied, "Yes, your honor."

Last month, the House Ethics Committee again deferred consideration of Grimm's alleged violations of campaign finance law to the Department of Justice. Grimm pleaded not guilty to a 20-count indictment last April stemming from allegations of fraud and misconduct tied to a New York restaurant he co-owned before taking office.

Grimm is also alleged to have solicited and accepted prohibited campaign contributions, caused false information to be included in campaign finance reports and allegedly made a deal with a foreign national to collect campaign contributions in exchange for help getting a green card.

"As an elected official, Grimm was responsible for deciding how taxpayers' money should be spent, yet he chose not to pay his fair share of taxes while operating his business," George Venizelos, Assistant Director in Charge at the New York Field Office, wrote in a statement. "Adding insult to injury, while serving as a Member of Congress, Grimm lied under oath in an effort to conceal his criminal activity. The public expects their elected officials at all levels of government to behave honorably, or at a minimum, lawfully. As his guilty plea demonstrates, Grimm put self-interest above public service."

Grimm holds a unique position in Congress: He is the only member of the House majority to represent New York City. But he also is a fairly typical species in Big Apple politics -- a ranking elected official hauled into criminal court by the FBI. In the last five years, the city has seen an embarrassing parade of pols arrested, capped off by a bipartisan plot to try and rig the GOP nomination for mayor.

Plea negotiations had dragged on for months. Sources indicated the case against Grimm was "solid" but "not good for the bureau" given Grimm's history as a former FBI agent.

Barring any developments, Grimm will be sworn into a third term in office on January 6.

Even before the court appearance, Democrats seized on the expected admission of guilt, calling on Grimm to resign from his seat in the House of Representatives.

"Now that the election is over, Congressman Grimm is finally admitting the truth to his constituents," House Minority Leader Nancy Pelosi, D-California, noted in a written statement. "Clearly, Speaker Boehner must insist that Congressman Grimm resign immediately."

House Speaker John Boehner's spokesman Michael Steel said Boehner “won't have any announcements until the Speaker discusses the matter with Mr. Grimm."

Grimm said he has had communication with GOP leadership but he refused to comment on those conversations. Members of Congress do not automatically forfeit their office upon conviction of a felony.

The two-term congressman gained national notoriety after he threatened to throw NY1/Time Warner Cable News reporter Michael Scotto off the Cannon Rotunda balcony following the president’s State of the Union address last January. Scotto was also in the courtroom today, seated in the front row.

ABC News' Mike Levine and Josh Margolin contributed to this report.