PROVIDENCE, R.I. (AP) — Federal highway regulators have told state officials that if the Pawtucket Red Sox build a stadium on land that was supposed to be a park, the land will have to be sold at fair market value first, a requirement that could add millions to the bottom line.

The new owners of the PawSox are pushing to build a stadium on prime riverfront land that used to be the site of Interstate 195. The I-195 Commission bought most of the land and is reselling it, although some was given for free for use as a public park.

The state Department of Transportation wrote to the Federal Highway Administration at the request of the I-195 Commission, which asked about the requirements for the land.

The federal agency responded Aug. 13, telling the transportation department that the land given to the commission for free has a stipulation on the deed that it remains open space.

Any change in use would require the land to be first returned to the department of transportation and sold at fair market value, the letter states.

The team’s original proposal called for building a Providence stadium on a 5-acre parcel designated as open space and surrounding land.

The current market value of the land is not clear. The 24 parcels of land freed up from the relocation of Interstate 195 were sold to the commission and Johnson & Wales University for $43 million in 2012, according to the Federal Highway Administration, and the state transportation department received the money for federal highway work.

The commission in January agreed to sell a smaller parcel that is not on the waterfront for $750,000. The 5-acre riverfront parcel eyed by the PawSox is 15 times that size.

Sharon Steele, a real estate agent and consultant who is vocally opposed to the stadium, said it’s unclear how much the land would be assessed at.

“That is the million dollar question. It is riverfront land and they’re not making any more riverfront so it’s worth as much as anybody will pay for it,” she said.

A spokesman for the Federal Highway Administration confirmed on Tuesday that if the land does not remain as public open space, then the land goes back to transportation department to be sold and the state keeps the money for federal highway work.

The agency recommended that the transportation department have the properties appraised. It also told the department a new federal environmental review would not be needed, but that the land use plan would need to be updated.

Modifying a land use plan is not as lengthy of a process as a full environmental review, but it does require input from the agencies involved and public hearings.

Charles St. Martin, a transportation department spokesman, said it has not begun work on a land use plan or conducted an appraisal.

A commission spokeswoman said Thursday that they’re reviewing the Federal Highway Administration’s letter. Dyana Koelsch said there are various open questions regarding stakeholder agreement and regulatory approval, and all of the various issues need further attention.

On Wednesday, PawSox principal owner Larry Lucchino toured another parcel near the I-195 land, Victory Place, which has been pitched by some members of the public as an alternative stadium location.

PawSox spokeswoman Patti Doyle said on Thursday that Lucchino was not looking at alternative sites and is still focused on the riverfront land.

The team’s original proposal, asking for $120 million in state subsidies, died after facing strenuous public opposition. The team is working with the state to renegotiate a deal.