WASHINGTON — New York Rep. Chris Collins announced Monday he is resigning from Congress following reports that he is expected to plead guilty tomorrow on criminal insider-trading charges.

He will appear in Manhattan federal court Tuesday, more than a year after he was indicted on insider-trading related to his investment in an Australian biotech firm: Innate Immunotherapeutics Limited.

Collins told House Speaker Nancy Pelosi in a letter that he will end his term “effective immediately.”

Pelosi’s office responded in a statement that they “are in receipt of a letter of resignation. It will be laid down on the House Floor tomorrow during pro forma. Resignation will be effective at that time. We release the letter at that time as well.”

Collins, a fourth-term congressman, was the first sitting member of Congress to endorse Donald Trump for president in the 2016 race, and narrowly won re-election last November despite being under indictment.

The 27th district is currently a Republican stronghold, with President Trump claiming victory there by 24 points in 2016. It covers the mostly rural areas between Buffalo and Rochester and is the state's most Republican-heavy district.

Nate McMurray, the Democratic supervisor of the town of Grand Island who narrowly lost to Collins last year, is rerunning for the seat in 2020, as well as several Republican candidates, including state Sens. Chris Jacobs and Robert Ortt, and attorney Beth Parlato.

Collins is accused of tipping his son and several others off to private information that came from Innate Immunotherapeutics Limited regarding trials for a drug meant to treat a form of multiple sclerosis.

This allowed his son and others to sell off their stock before the value plummeted and the news about the unsuccessful trials were made public.

At the time, Collins owned 16.8% of the company's shares and sat on its board. Though he did not ultimately sell off his stock, his son and allies did, according to prosecutors.

Collins' co-defendants, his son and another family member, are also set to change their pleas later this week, according to court filings.

It would be up to New York Gov. Andrew Cuomo to set a special election to fill the seat.

Contributing: Jon Campbell