Andrews has represented the heavily Democratic Philadelphia-area suburbs since 1990.

Andrews has been under investigation by the House Ethics Committee for allegedly misusing campaign funds for personal use. Allegations include that he used campaign funds to pay for a family trip to Scotland. A special four-member investigative subcommittee was appointed to look into the case a year ago, but it is unclear if that panel had made any recommendations for action to the full Ethics Committee.

( PHOTOS: Who’s leaving Congress?)

The New Jersey Democrat began quietly telling friends on Monday night of his decision to resign, sources said, and he plans an announcement at 11:30 a.m. at his Haddon Heights, N.J. office.

State Sen. Donald Norcross may announce as early as today that he will run for this seat, Democratic sources said.

( Also on POLITICO: Andrews backs Norcross for seat)

Andrews, 56, is an ally of Speaker Nancy Pelosi (D-Calif.). She appointed him to be policy co-chair of the Democratic Steering Committee last year.

Some Democrats had been quietly complaining that Andrews was next in line to be ranking member of the Education and Workforce Committee in the next Congress after Rep. George Miller (D-Calif) announced his retirement.

( PHOTOS: 10 must-watch House races in 2014)

But with the ethics problems hanging over his head, it was unclear if Andrews could get that post.