The House Ethics Committee revealed Thursday that Congressman David Schweikert and chief of staff Oliver Schwab have been under investigation by a nonpartisan congressional watchdog.

Schwab allegedly received $165,000 in consulting fees from Schweikert's campaign committee, more than five times the congressional limit on outside income for a staffer.

The committee's announcement Thursday indicates the independent Office of Congressional Ethics determined there was substantial reason to believe ethics violations occurred.

Schweikert is a Fountain Hills Republican seeking a fifth term in office this fall.

Neither the House Ethics Committee nor the OCE will discuss the nature of the investigation. It follows reports in the Washington Examiner last year of Schwab's generous spending while traveling and a complaint that Schwab exceeded how much money he can earn from a second job.

The complaint, filed with the OCE by a Democratic activist living in Schweikert's district, states Schweikert's campaign committees also accepted illegal in-kind campaign contributions from Schwab.

Schweikert is a Fountain Hills Republican seeking a fifth term in office this fall.

After a border tour Thursday with Homeland Security Secretary Kirstjen Nielsen, Schweikert told reporters the allegations involved a "bookkeeping issue."

"We've taken all of our documents over to the House Ethics (Committee) and looks like things are fine," Schweikert said.

"We had some reporting issues with the previous compliance firm. It's all been fixed now. So now we'll just wait for our stamp of approval."

The House Ethics Committee said it would announce a decision on the investigation no later than Nov. 14 - a week after the general election.

The Associated Press contributed to this report.