The United States is threatening to impose tariffs on $4 billion in European Union (EU) goods over a lengthy dispute involving subsidies for the world's two largest plane manufacturers.

The U.S. Trade Representative's Office (USTR) released a list Monday of additional products the U.S. could target in addition to the $21 billion worth of EU goods that were announced in April.

Among the list of additional goods are a variety of metals, olives, Italian cheese and Scotch whiskey. The USTR said the supplemental list was compiled in response to public comments, but did not elaborate.

The U.S. and the EU have traded threats of retaliatory tariffs on planes, food and other items in a nearly 15-year spat at the World Trade Organization (WTO) over illegal aircraft subsidies given to U.S. plane maker Boeing and European rival Airbus.

Senior officials from Boeing and a U.S. aerospace lobbying group urged the U.S. government last month to customize any new EU tariffs to avoid hurting American manufacturers.

Boeing sign is seen on the aircraft manufacturer's Center in Crystal City, Arlington, Virginia. (Photo: Diaa Bekheet). The aircraft manufacturers did not immediately comment on the latest threat of U.S. tariffs.

The aircraft manufacturers did not immediately comment on the latest threat of U.S. tariffs. But Lisa Hawkins of the Distilled Spirits Council of the United States denounced the latest threat by U.S. President Donald Trump's administration.

"U.S. companies, from farmers to suppliers to retailers, are already being negatively impacted by the imposition of retaliatory tariffs by key trading partners on certain U.S. distilled spirits ...and these additional tariffs will only inflict further harm," she said.

Washington and Brussels have accused each other of unfairly subsidizing their respective domestic airline manufacturers in a trade dispute.

The WTO has found that Boeing and Airbus have received billions of dollars in subsidies and is expected to rule on the U.S. sanctions proposal in coming weeks.

The USTR said it would hold a hearing on the latest U.S. proposal on August 5.