Rep. Michael Grimm announced late Monday that he plans to resign, one week after the Republican Staten Island congressman admitted to federal tax evasion.

Grimm, who was re-elected to a third term representing New York's 13th District in November, said in a statement that he would step down effective Jan. 5.

"This decision is made with a heavy heart, as I have enjoyed a very special relationship and closeness with my constituents, whom I care about deeply," he said. "The events which led to this day did not break my spirit, nor the will of the voters. However, I do not believe that I can continue to be 100% effective in the next Congress, and therefore, out of respect for the Office and the people I so proudly represent, it is time for me to start the next chapter of my life."

Grimm pleaded guilty on Dec. 23 in federal court in Brooklyn to one count of aiding in the filing of a false tax return. He had been accused of hiding more than $1 million in sales and wages while running a Manhattan health-food restaurant.

Under the plea agreement, he could face up to three years in federal prison. His sentencing is set for June 8.

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Following his guilty plea, Grimm initially said he planned to continue serving in the Congress.

"As long as I'm able to serve, I'm going to serve," he said last week. "As of right now I'm still in a capacity to serve, and that's exactly what I plan on doing."

The House won't formally recognize the vacancy until after the new Congress convenes on Jan. 6. Grimm's resignation will reduce the GOP majority in the new Congress from 247 seats to 246.

A senior Democratic source told Fox News that even though Democrats have eyed the seat, the party believes it will be difficult to pick it up in a special election.

The indictment against Grimm alleged the tax fraud began in 2007 after he retired from the FBI and began investing in a Manhattan eatery called Healthalicious. It accused him of underreporting more than $1 million in wages and receipts to evade payroll, income and sales taxes, in part by paying immigrant workers, some of them in the country illegally, in cash.

In court last week, Grimm acknowledged that while operating the restaurant, "we underestimated gross receipts and used money to pay employees off the books. The tax returns were false."

The case stemmed from an investigation of Grimm's campaign financing. He was never charged with any offense related to his campaign, but a woman romantically linked to him pleaded guilty in September to lining up straw donors for his 2010 run. Grimm has denied knowledge of any fundraising improprieties.

Grimm, 44, made headlines in January after telling a local cable TV news station reporter he wanted to throw him off a balcony in the Capitol for asking about the campaign finance inquiry.

Fox News' Chad Pergram, Melanie Schuman, Mike Emanuel and The Associated Press contributed to this report.