Donald Trump vowed to issue an executive order targeting offshore wind development if he wins a second term as president, making his most explicit threat yet toward the growing industry.

The presumptive Republican nominee derided offshore wind projects as lethal for birds and whales during his oceanfront rally Saturday in Wildwood, New Jersey, and committed to take action.

“We are going to make sure that that ends on day one,” he said. “I’m going to write it out in an executive order.”

While Trump has made no secret of his animus toward wind power, he had adopted a mostly hands-off posture during his first term in the White House. The remarks in New Jersey suggest he may take a more aggressive stance if given a second.

While Trump wasn’t specific, a president could issue an executive order directing a fresh study of the impact of offshore wind and halting the permitting of new projects in the meantime.

President Joe Biden used a similar approach to order a moratorium on offshore oil leasing during his first week in the White House.

Developers say offshore wind is set to deliver big economic dividends — and potentially $25 billion in annual output — throughout the U.S., as it drives demand for specialty steel, new ships and other equipment. The same day Trump was speaking in New Jersey, a new American-built boat to service U.S. offshore wind farms was christened in New Orleans.

Trump’s accusations Saturday included that offshore wind farms “kill the whales” because of ocean floor surveys done to plan construction. “Nobody even knows what it is,” he said, “but I think in 20 years one whale washed up on shore, and then where they have these things, they come up all the time, dead.”

While there has been an uptick in humpback whale deaths since 2016 — including the endangered North Atlantic right whale — U.S. scientists say many of the fatalities can be attributed to boat strikes or entanglements. There is no evidence linking offshore wind development to whale deaths, though government scientists have raised concerns about the consequences of greater noise, more vessel traffic and habitat changes tied to the industry.

Offshore wind advocates say Trump would be better off embracing a new source of American-made energy.

“The fundamental value proposition of offshore wind remains clear: Safe, reliable, large-scale renewable energy production, good-paying union jobs, and significant public health and economic benefits,” said Paulina O’Connor, executive director of the New Jersey Offshore Wind Alliance.

“By capitalizing on this emerging American industry, we remain in prime position to maximize the benefits of offshore wind for decades to come through U.S.-based jobs, manufacturing and investment.”