(CNN) New York Rep. Chris Collins submitted his resignation from Congress on Monday, one day ahead of his expected guilty plea to federal charges in an insider trading case, according to the House Speaker's office, court documents and a person familiar with the matter.

Collins sent a letter of resignation Monday to the office of House Speaker Nancy Pelosi, according to her spokesman, who said Collins's resignation will be effective Tuesday.

He faced reelection in 2020. While a guilty plea wouldn't by law have caused him to immediately lose his congressional seat unless the House of Representatives had expelled him, a step that would have required a full vote of the House, it would have made for a challenging reelection bid.

The Republican congressman narrowly retained his seat in western New York in 2018, beating his Democratic opponent by less than half a percentage point.

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