(CNN) — (CNN) -- Democratic Sen. Bob Menendez questioned decisions made by federal health officials about his friend and major donor Salomon Melgen, an eye doctor tied to a recent scandal surrounding Menendez, a source close to the senator confirmed Thursday.
First reported by The Washington Post, Menendez "raised concerns" with the officials' conclusion that Melgen had overbilled the federal government by $8.9 million in Medicare and Medicaid payments when treating patients at his West Palm Beach clinic.
In 2009, the New Jersey senator first contacted federal authorities about the government's assessment of Melgen. Taking the issue up with the director in charge of Medicare payments, Menendez claimed it was unfair to penalize the doctor "because the billing rules were ambiguous."
The Post, however, reported that Melgen was billing the government three to four times for injections from a single vial to treat macular degeneration.
Menendez again met with federal officials in 2012 to dispute the auditors' appraisal of Melgen's billing. The agency had demanded that Melgen repay the nearly $9 million in overbilling.
When asked by CNN Thursday about the new billing allegations, Melgen declined to immediately answer the question but said he would later return with a comment.
Separately, Melgen has made headlines recently for providing plane rides for Menendez in 2010 to the Dominican Republic--trips the senator didn't pay for until January of this year.
Menendez told CNN in an exclusive TV interview earlier this week that the pay discrepancy--worth nearly $60,000--was simply an oversight.
"I was in a big travel schedule in 2010 as the chair of the (Democratic Senatorial Campaign Committee), plus my own campaign getting ready for a re-election cycle and in the process of all of that, it unfortunately fell through the cracks," he told CNN's Dana Bash, adding that when it came to his attention the payment had not taken place, he "personally paid" for it in order to meet his obligation.
Menendez, however, has also been in some hot water for raising questions before administration officials about a port security contract for a company in which Melgen has a stake. The company had a contract to screen cargo that went through Dominican ports, but Menendez argued last July during a Senate subcommittee hearing that Dominican authorities didn't want to "live by" the contract.
Asked if he used his influence to help Melgen, Menendez told Bash: "I have always advocated for issues and I have advocated for policies, and that's what I have done across the board."
Melgen's offices were raided by FBI agents and health care investigators last week as part of a fraud probe, fueling further speculation about his ties to Menendez. An aide to the senator, however, told the Post that Menendez was unaware Melgen was under formal investigation for possible fraud until the raid last week.