The U.K. isn’t alone in prolonging a Brexit battle in the hope of a better deal—French customs officers are also taking negotiations to the brink.

Traffic jams built up again at French ports and Eurostar advised passengers from Paris to London not to travel “unless absolutely necessary” as customs officers caused delays Thursday by working to rule.

Unions have rejected the government’s 14 million-euro ($16 million) offer to boost salaries due to the extra workload expected from Brexit. The head of the customs office was due to meet with unions again Thursday, budget minister Gerald Darmanin said.

The government is under pressure to find a solution as around 60 percent of all goods and people moving between the U.K. and the EU go through French harbors and the Channel Tunnel rail link. But France is also trying to curb public spending as its budget deficit is one of the highest in Europe.

“It’s normal in this particular situation that unions try to get things they haven’t got before,” Darmanin said on France Info radio Thursday. “They will have to choose between raising staffing and increasing wages.”

Eurostar canceled four trains Thursday due to the delays from customs officers working to rule. On its website, the CGT union said there were delays of two hours at Paris Gare du Nord and traffic jams on major roads leading to ports in the north of France.