The House Ethics Committee announced on Friday that the Office of Congressional Ethics had referred a case involving Reyes to the committee at the end of August.
The committee did not reveal the topic of the inquiry, but a joint statement from the panel's top lawmakers, Rep. Jo Bonner, R-Ala., and Linda Sanchez, D-Calif., said they would continue a period of fact-finding until Nov. 28.
A report in March from the group Citizens for Responsibility and Ethics in Washington singled out Reyes as among the biggest users of his campaign account to reimburse himself for expenses and to pay family members, citing more than $400,000 in reimbursements over the last two election cycles.
Jose Borjon, Reyes' communications director, said the congressman has behaved "with the highest level of ethics" and "is fully cooperating with their review, and expects this referral to be disposed of quickly."
He declined to discuss the topic of the inquiry.
In May, Reyes, an eight-term incumbent, lost a primary to former El Paso councilman Beto O'Rourke. Reyes lost despite the backing of Presidents Obama and Clinton.
This post, originally published at 4:52 p.m., has been updated.
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