Democratic Representative Dennis Cardoza of California said he would resign on Wednesday, a move he told a local newspaper was due to family concerns.
"Tomorrow, I will be submitting my formal letter of resignation from Congress to Governor Jerry Brown and Speaker John Boehner, effective midnight August 15th," Cardoza said in a statement released by his office on Tuesday.
Cardoza, who represented part of California's agricultural Central Valley for five terms, said last year he would not seek re-election. He was first elected to the House of Representatives in 2002.
The statement gave no reason for the abrupt resignation, but in an interview with the Merced Sun-Star in his home district, Cardoza cited concerns over his three children.
"In light of the fact that nothing is going to happen for the rest of the year, and in light of the fact that [my wife] and I are facing increasing parenting challenges, this seemed the right time to make this move," Cardoza told the newspaper.
The House is only scheduled to be in session for another 13 days before the Nov. 6 election.
Cardoza has taken a position at the law firm Manatt, Phelps & Phillips as a managing director in its government affairs and public policy practice, and will be based in Washington, D.C., the firm said in a statement.
Cardoza, who served on the House Agriculture and Foreign Affairs committees, said in a statement he was pleased to join the firm.
Cardoza's office told Reuters he would have no further comment.
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