A grand jury is investigating Sen. Robert MenendezRobert (Bob) MenendezCongress must provide flexible funding for owners of repeatedly flooded properties Senate ethics panel resumes Menendez probe after judge declares mistrial Judge declares mistrial in Menendez bribery case MORE’s (D-N.J.) role in advocating for the business interests of Salomon Melgen, a political donor and Florida eye doctor, The Washington Post reported Thursday evening.

“Three people aware of the probe” told the newspaper that federal agents have questioned witnesses. The sources spoke on the condition of anonymity, the Post said. 

Two people briefed on the probe told the Post that the federal grand jury in Miami has issued subpoenas for Melgen’s business and financial records.

“I welcome any review, because I believe, at the end of the day, that my actions have been appropriate,” the senator told the Post.

Menendez has steadfastly maintained his innocence against charges that he has improperly helped his “friend and political supporter.”

"Every day, more evidence emerges that the false smears against Senator Menendez are nothing but an elaborate campaign orchestrated by Republican political operatives," his office said in a statement emailed to The Hill on Friday. "As we have said all along, we welcome any review because Senator Menendez’s actions have always been appropriate, and we believe the facts will confirm that."

The Post previously reported Menendez admitted to contacting officials at the Centers for Medicare and Medicaid Services to raise questions about a finding Melgen had overbilled the government by nearly $9 million.

The New York Times, meanwhile, has reported Menendez discouraged the federal government from donating port security equipment to the Dominican Republic, which would have undermined a contract a company owned by Melgen had to provide security screenings.

And the Associated Press reported earlier this month that Menendez sponsored legislation to boost tax credits and grants to companies that converted their vehicle fleets to use alternative fuels that would have financially benefited Melgen.

The Senate Ethics Committee is also looking into claims that Menendez acted improperly by flying to the Dominican Republic on Melgen’s private plane.

Menendez recently reimbursed Melgen’s company $58,500, the cost of two previously undisclosed trips from personal funds.

Melgen took him on at least three trips to the Dominican Republic aboard his private plane in 2010.

Earlier this month, Menendez urged reporters to investigate who was behind the accusations that he had sex with Dominican prostitutes on those trips with the same gusto they brought to scrutinizing his relationship with Melgen.

This story was updated at 9:39 a.m.