The European Union is poised to move next week to impose tariffs on $4 billion of US imports in retaliation for US subsidies for planemaker Boeing, EU diplomats said, teeing up an eleventh-hour showdown with US President Donald Trump.

A majority of EU governments have backed imposing the widely expected tariffs once EU trade ministers meet next Monday - the latest twist in a transatlantic trade saga that has spanned 16 years and four US presidents.

Democratic presidential candidate Joe Biden is edging closer to victory in the US election, but Republican Trump would remain president until Jan. 20 and has plenty of leeway to increase US tariffs on Europe that were imposed in a parallel case over subsidies for Airbus.

US Trade Representative Robert Lighthizer last month warned any EU tariffs would "force a US response" and Trump has threatened to "strike back harder"..

Brussels views its own tariffs - authorized by the World Trade Organization last month - as important leverage in negotiations to end a dispute that began in 2004.

"I would expect the tariffs to be imposed next Tuesday or Wednesday," an EU diplomat said.

In October 2019, Washington imposed tariffs on Airbus planes and other European products from cheese to olives and single-malt whisky. Combined, the two cases represent the world's largest ever corporate trade dispute.

Washington argues there is no legal basis for EU tariffs because underlying subsidies to Boeing have been repealed. European officials argue it is only the WTO that can decide on compliance and that last month's green light stands.

Both sides accuse the other of failing to obey WTO rulings but are seen as determined to maximize their positions ahead of probable negotiations.

If Biden wins, the avowed transatlanticist is expected to work quickly to mend fences with Brussels on a host of issues, and could use talks over the aircraft subsidies as a gesture of goodwill as he tries to build a more united front against China.