Rep. Trent Franks, R-Ariz., is expected to announce his resignation Thursday evening, multiple Republican sources told NBC News.
The 8th District congressman did not confirm or deny any plans to resign.
Franks told Roll Call that a statement would be forthcoming.
If Franks steps down, Arizona Governor Doug Ducey would call a special election to fill the seat.
He was expected to make a statement Thursday; the aide was not authorized to discuss the matter before Franks' announcement. The Republican said the congressman had apparently been making plans to run for Senate in 2012, but abruptly canceled those plans.More news: Goldstone Followed Up On Trump Tower Meet With Trump Aide, His Client
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Representing a solidly-Republican swath of Arizona, north of Phoenix, Franks built a reputation as a hard-line conservative since joining Congress in 2003.
One Arizona Republican reportedly said not many people would be "surprised" if he resigned. But no revelations were aired in the aftermath of the decision, and Franks went on to assume the chairmanship of a House Judiciary subcommittee.
It was not immediately clear why the GOP member is planning to leave his seat.
Trent is now serving his eight term in Congress - he was first elected in 2002. The general election must be held no less than 50 and no more than 60 days after the primary.