On Monday, Harley-Davidson said Belgium’s Economic Ministry, on behalf of the EU, had notified the company that it was revoking an agreement that allowed the business to supply Europe with certain motorcycles produced at its international manufacturing facilities at tariff rates of 6%.

Harley-Davidson said the EU ruling would apply to its entire lineup and subject all products—regardless of origin—to a 56% import tariff in the trade bloc.

The European Commission, the EU’s executive arm, didn’t immediately respond to a request for comment.

Harley-Davidson had lowered its EU tariff bill by sending motorcycles to Europe that were made in Thailand. With the end of that arrangement, the company now finds itself battling EU trade authorities over a tariff imposed on motorcycles that are no longer produced in the U.S.

The motorcycle maker said it plans to lodge an immediate legal challenge to what it called an unprecedented decision that “underscores the very real harm of an escalating trade war to our stakeholders on both sides of the Atlantic.”

Harley-Davidson received word of the EU’s tariff increase late Friday, a person familiar with the matter said.

The company also had positive news to offer Monday with a sales update. It said a 30% increase in motorcycle volumes in North America helped sales exceed expectations for the first quarter. It also raised its 2021 forecast for motorcycle revenue to growth of 30% to 35%, from a previously projected 20% to 25%.

Harley-Davidson shares were up 12% in midday trading.

While the EU’s original round of tariffs hit other high-profile U.S. goods, such as jeans made by

Levi Strauss

& Co. and Kentucky bourbon, vocal support from then-President Donald Trump pushed Harley-Davidson into the spotlight as a U.S. victim of the trade barbs exchanged in recent years between the U.S. and Europe and China.

Harley-Davidson said in 2018 that EU tariffs would raise the cost of each bike shipped to the trade bloc from the U.S. by about $2,200. Rather than raise prices, the company said it would shift production of motorcycles for the EU market to outside the U.S., prompting Mr. Trump to accuse the company of raising the white flag.

More recently, the U.S. has ended some import tariffs. For instance, in March it canceled levies on British luxury products, including Scotch whisky, that had been imposed as part of a dispute over subsidies to

Airbus SE,

the European aircraft manufacturer.

Europe, the Middle East and Africa had been among Harley-Davidson’s largest markets outside of the U.S., but its first-quarter results showed almost 3,000 few motorcycles sold in the sales region, marking a 36% decline from a year earlier.

The company attributed the decline to shipping delays related to the pandemic and its decision to stop selling some popular motorcycle models in the region. Harley-Davidson will soon offer a new motorcycle known as the Pan America and designed for on-road and off-road use. Company executives anticipate the model will be popular in Europe.

The EU tariff decision comes at a time when the company has curtailed sales activities in lesser foreign markets to focus on North America, Europe and Japan. Harley-Davidson is in the midst of overhauling its sales and production strategies under Chief Executive

Jochen Zeitz,

a longtime director picked for the top post early last year. The company in 2020 slashed production of motorcycles as part of a plan to reduce inventories of bikes at dealers and boost prices for used models.

—Bob Tita contributed to this article.

Write to Alistair MacDonald at alistair.macdonald@wsj.com and Colin Kellaher at colin.kellaher@wsj.com