EU Trade Commissioner Valdis Dombrovskis has warned that a Chinese blockade of Lithuania's exports over a dispute about Taiwan was increasingly affecting firms from other EU countries.
Mr Dombrovskis told German daily Die Welt that the Commission had been able to verify Lithuanian claims about the blockade.
"It causes us concern that we are increasingly getting reports from other member states about blocked imports" by China as well, he said.
"Apparently Chinese customs is not processing goods from other EU countries if they contain parts from Lithuania."
Mr Dombrovskis said there were now "many cases in which imports from Lithuania and the EU are being stopped at Chinese ports and the number is increasing daily".
The Commissioner said the blockade appeared to affect both large and small shipments.
"Given the massive daily trade volume between the EU and China, it's not surprising that the amount is growing fast," he said.
Mr Dombrovskis said the Commission was using political and diplomatic channels to try to resolve the dispute and that he had spoken directly with China's EU envoy about the matter.
But should those efforts fail, he said his staff was preparing a complaint with the World Trade Organization.
"We would prefer an amicable settlement for this problem, that's obvious," he said, adding "we have to be prepared for these efforts being unsuccessful".
Last month, China downgraded diplomatic ties with Lithuania and stopped issuing visas there in protest at Vilnius's decision to allow Taiwan to open a representative office under its own name.
China baulks at any official use of the word Taiwan lest it lend a sense of international legitimacy to the island, which China considers part of its territory.
Several Lithuanian companies and business leaders complained this month that China was blocking their exports as their goods were not clearing customs in the country.