The FBI and IRS are investigating Rep. David Rivera over payments that a casino company may have made to a company owned by the Florida Republican’s mother, the Miami Herald reported Thursday.

His campaign office slammed the Herald’s credibility.

“The Miami Herald story is a recycling of the same old, false, misleading, unattributed, and unsubstantiated reporting that has characterized their coverage thus far,” it said in an email. “Contrary to the Herald’s insinuation, Congressman Rivera has not been contacted by the FBI or IRS on any matter whatsoever.”

The federal probe is separate from a state-level investigation of Rivera’s finances by the Florida Department of Law Enforcement and the Miami-Dade Office of the State Attorney over an undisclosed $130,000 loan that Rivera received from his mother’s company. The Congressman says it has since been repaid.

The FBI and IRS investigations are focusing on a $1 million contract between Magic City Casino, once known as Flagler Dog Track, and Millennium Marketing, which is co-owned by Rivera’s mother.

A Rivera spokesman told the Herald that the agencies had not contacted the Congressman and that he denied receiving any money from the casino or his mother’s marketing agency.

Rivera is a top target for Democrats, who see the rumors of wrongdoing as a way to regain a House seat. The former state Representative won with just 52 percent of the vote in 2010, and his fundraising in recent months has lagged. His campaign brought in only $35,000 in the second quarter and had just $62,000 in cash on hand at the beginning of June, according to a Federal Election Commission filing.

On Wednesday, his first Democratic challenger stepped forward. State Rep. Luis Garcia, a former fire chief, announced he would campaign in Rivera’s Miami-area district.

Joshua Miller contributed to this report.