Developers behind the wind project off the coast of Ocean City have just about everything they need to start building. The wind farm cleared a final federal hurdle in December and, last month, developers got the paperwork they needed from Maryland regulators, too.

At least, they thought they did.

Last week, the U.S. Environmental Protection Agency intervened, sending a letter to Maryland regulators informing them that the state’s air quality permit isn’t valid.

While the letter dings Maryland regulators for a procedural aspect of their permit, it comes as President Donald Trump has attempted to block and roll back offshore wind development across the country.

A budding American offshore wind industry sees huge potential off the coast of Maryland but has yet to put any turbines in the water there.

The only Maryland development with federal clearance to move forward, by Baltimore-based U.S. Wind, is fighting several other skirmishes: A coastal Delaware county has tried to block the wind farm from tying into the power grid there, while Ocean City, local fishermen and other nearby jurisdictions have sued the U.S. Department of the Interior over the project’s siting roughly 10 miles offshore.

In a statement, the Maryland Department of the Environment did not indicate whether it plans to stand by its permit but said it is reviewing the EPA letter.

“MDE is committed to ensuring all our permit processes are transparent and in accordance with the law,” said spokesman Jay Apperson.

U.S. Wind, meanwhile, said it’s confident its permits are valid.

“We’re very committed to delivering this important energy project to the region,” said Nancy Sopko, vice president of external affairs for U.S. Wind, in a statement. “The state needs all the new sources of electricity we can build in order to keep prices affordable for homes and businesses.”

The EPA’s letter focuses on a provision of the MDE permit that sends any efforts to appeal the approval to a state board.

Maryland issued the permit under delegated authority of the federal Clean Air Act, and the EPA argues in its letter that any effort to appeal the permit should go to the Environmental Appeals Board, an independent division of the EPA.

To comply, Maryland regulators must reissue its permit to US Wind. Failure to remedy the appeals process issue “could result in invalidation of the permit on appeal,” Mid-Atlantic EPA Administrator Amy Van Blarcom-Lackey wrote to state regulators.

While U.S. Wind balked at the EPA letter, some cheered the federal intervention.

U.S. Rep. Andy Harris, a Republican who represents the Eastern Shore and Ocean City, has been an outspoken opponent of the wind project, often attacking U.S. Wind, which is based in Baltimore but mostly owned by an Italian energy company, as a foreign corporation trying to take advantage of American tax incentives.

In a statement responding to the EPA letter, the congressman said the MDE decision “showed both incompetence and a disregard for public input” from local residents.

“The EPA has confirmed what many of us knew for years — this project was approved with glaring procedural and legal flaws," he said. “For many years, my constituents across the First Congressional District have been overwhelmingly clear: they do not want offshore wind off their coast.”

U.S. Wind has leased a sprawling 80,000 acres off the Maryland-Delaware coastline. The company is pursuing a multiphase development there. The first two phases would generate a combined 1,100 megawatts of electricity, enough to power hundreds of thousands of homes in the region.