BRUSSELS (AP) — The European Union will link any access to its market for British products directly to the access that EU boats will be given to U.K. waters, the bloc’s chief negotiator said Monday.

EU negotiator Michel Barnier underscored the difficulties of the trade negotiations with Britain ahead for the rest of the year when he highlighted the small but emblematic fisheries industry, which was a key issue in the protracted Brexit process in the United Kingdom too.

Barnier told France Inter radio that “there will be no trade deal with the British if there is no reciprocal access deal for our fishermen.”

Barnier said “we will negotiate access to the British territorial waters for European fishermen at the same time that we negotiate access to European markets for British fisheries products. I hope I make myself clear.”

Overall, the EU is willing to grant the U.K. the fullest possible access to its lucrative market of some 450 million consumers but only if Britain abides by EU standards on such things state aid, social legislation or environmental protections.

British Prime Minister Boris Jonhnon has already indicated he does not want to make a binding commitment to remain in line with EU law, saying it was an essential principle in the move to walk away from the Union. Britain on Friday left the EU, becoming the first nation ever to do so.

The official break-up came last Friday and Johnson has said he wants a trade and cooperation deal by the end of the year, a time frame which the EU has called unrealistic.