US PRESIDENT Donald Trump said on Sunday that a planned boycott of iconic American motorcycle manufacturer Harley-Davidson for wanting to move some of its operations outside the United States would be “great.”

“Many @harleydavidson owners plan to boycott the company if manufacturing moves overseas. Great!,” Mr Trump wrote on Twitter Sunday, according to the New York Post.

“Most other companies are coming in our direction, including Harley competitors. A really bad move! U.S. will soon have a level playing field, or better.”

Mr Trump sent the tweet from his golf resort in Bedminster, New Jersey, where he hosted members of “Bikers for Trump” on Saturday afternoon.

Harley-Davidson executives said in June that they were planning to shift production of motorcycles being sold in European markets to overseas factories.

They said it was in response to retaliatory tariffs the European Union slapped on imported hogs after Mr Trump imposed levies on steel and aluminium imports from Europe.

Harley-Davidson said the EU’s tariffs would increase the cost of one of its bikes by $US2200 ($3000).

Some owners told the New York Times that the decision would end their decades-old relationship with the Wisconsin-based company.

“I’m riding my last Harley,” Gary Rathbun, a 67-year-old retired truck driver attending the legendary Sturgis Motorcycle Rally in North Dakota, told the newspaper.

“It was American made, and that’s why we stood behind them.”