WASHINGTON >> The Treasury Department’s internal watchdog is investigating whether Florida Gov. Ron DeSantis improperly used federal pandemic aid to fly migrants to Martha’s Vineyard as part of his effort to “transport illegal immigrants to sanctuary destinations.”

At issue is whether millions of dollars in interest earned on State and Local Fiscal Recovery Funds, disbursed through the American Rescue Plan, was used to facilitate the transport of about 50 Venezuelans from Texas to Massachusetts in mid-September, with a stopover in Florida on the way.

The recovery funds program has strict requirements on how the money can be spent. Documents indicate Florida officials paid Destin, Fla.-based Vertol Systems Co. $1.56 million for the Martha’s Vineyard flight and possibly for a flight to Delaware, the home state of President Joe Biden, that ultimately didn’t happen.

The inspector general’s office has audit work planned on “recipients’ compliance with eligible use guidance,” Treasury Deputy Inspector General Richard K. Delmar said in a letter addressed to Sen. Ed Markey, D-Mass., who requested the investigation.

“We plan to get this work underway as quickly as possible, consistent with meeting our other oversight mandates and priorities,” the letter said. Treasury does not have a confirmed inspector general.

Markey wrote to the inspector general’s office in September, shortly after DeSantis arranged the trip, which received wide publicity. The Florida governor said the migrants traveled voluntarily to Massachusetts.

“The use of federal COVID relief funds in this manner runs contrary to congressional intent and appears to violate federal law,” Markey and six other Massachusetts lawmakers wrote in a Sept. 17 letter to Delmar. Markey said DeSantis was “effectively using COVID-19 relief to score political points by exploiting vulnerable immigrants.”

The White House has called the trip to Martha’s Vineyard a “cruel, premeditated political stunt.”

Delmar did not indicate when the probe would be complete. Other law enforcement agencies throughout the U.S. have also launched investigations of migrant trips arranged by Republican lawmakers to Democratic strongholds.

The flight has also spawned an investigation by a Texas sheriff and two lawsuits. The Treasury Department referred questions to the inspector general’s office, which did not respond to a request for comment.