Rep. John Conyers, the longest-serving member of Congress, retired Tuesday amid sexual misconduct accusations from former staff members.

The 88-year-old Democrat from Detroit previously rejected calls from his party leaders, including Rep. Nancy Pelosi, to step down after a half-century career on Capitol Hill.

"I'm in the process of putting my retirement plans together," he told a Detroit radio show Tuesday morning from a hospital, where he was being treated for what his consultant has described as stress.

Later, he said: "I am retiring today." Conyers endorsed his son, John Conyers III, to replace him in Congress.

He later submitted a letter to Pelosi and House Speaker Paul Ryan, which read: "I have made the decision to retire from my position as the Member of the United States House of Representatives from Michigan's Thirteenth Congressional District effective today."

Conyers was the longest-serving member of Congress. He first got elected in 1964.

On Monday, Elisa Grubbs, who said she worked in Conyers' office from about 2001 to 2013, accused him of putting his hand up her skirt and rubbing her thighs when they sat in the front row of a church, according to The Associated Press. She added that she saw the congressman inappropriately touching other female staff members on "multiple occasions."

Another accuser, Marion Brown, reached a confidential settlement with Conyers but broke a confidentiality agreement to speak publicly about her allegations.

Conyers denies having acted improperly. He previously stepped down from his role as ranking member of the House Judiciary Committee. The House Ethics Committee is investigating the accusations.

Once Michigan Gov. Rick Snyder receives Conyers' resignation, he has discretion about when to call special primary and general elections to replace him, said Fred Woodhams, a spokesman for the Michigan secretary of state's office. The winner would serve the remainder of Conyers' term through January 2019.

In 2016, Conyers easily won the election to represent Michigan's 13th District, which includes parts of Detroit and its suburbs.

— The Associated Press contributed to this report