In the sprawling flatlands of Denmark’s Jutland peninsula, near the small town of Give, a family-owned company called Welcon has been gearing up to build giant, cylindrical wind turbine towers for a multibillion-dollar project.

The project, a wind farm called Empire Wind, is being built by the Norwegian energy giant Equinor in the waters off Long Island, N.Y. But those plans were thrown into disarray last month when the Trump administration, which is skeptical about offshore wind power, ordered an indefinite halt to construction.

The pause shocked Carsten Pedersen, who owns Welcon with his brother Jens, and the wind industry.

“It’s, in my opinion, a banana republic over there,” Mr. Pedersen said, referring to the chaotic blitz of policy changes coming from Washington. “You cannot just stop projects” whose developers have already put in years of work.

Welcon was tapped as a subcontractor to supply the towers for the project by Vestas Wind Systems, a leading wind turbine maker, which has its headquarters in Aarhus in Jutland.

If Empire Wind is permanently shut down, Vestas will lose a manufacturing order likely worth around $1 billion for 54 of its latest turbines, which have blades nearly 380 feet long. The contractors would probably receive some compensation from Equinor.

The wind industry is crucial to Europe’s ambitions to tackle climate change and enhance energy security, but three months into President Trump’s second term in office, industry executives are reassessing their approach to renewable energy.