The U.K. said it would retaliate with more rigorous checks on fishing activity in its waters if France follows through with its own threat to disrupt trade in a bitter dispute over post-Brexit fishing access.

The French threats would put the European Union in breach of its Brexit agreements, U.K. Prime Minister Boris Johnson’s office said in a statement on Friday. The British would then consider launching dispute settlement proceedings that would include “rigorous enforcement processes and checks on EU fishing activity in U.K. territorial waters.” 

The French government has said its vessels are being wrongly denied licenses to fish in British waters, and earlier this week threatened to blockade U.K. trawlers and raise energy prices in the British Channel Islands if more fishing licenses aren’t granted by Nov. 2.

The U.K. summoned the French ambassador on Friday to explain the “disappointing and disproportionate” threats. 

Talks between the two sides will continue through the weekend, according to officials. 

U.K. Prime Minister Boris Johnson is traveling to the Group of 20 leaders summit in Rome on Friday, where French President Emmanuel Macron will also be in attendance. The two may meet on Sunday, according to Macron’s office. French authorities also seized a British trawler near Le Havre on Wednesday for not having a permit, another sign of escalating tensions.

Separately, U.K. Brexit minister David Frost and European Commission Vice-President Maros Sefcovic met in London to discuss ways to resolve another dispute over trade arrangements in Northern Ireland. Those talks will continue next week, with Frost traveling to Brussels on Nov. 5.