BRUSSELS (Reuters) – The European Union’s Brexit negotiator, Michel Barnier, will update the bloc’s 27 national envoys on the latest on Brexit at 1500 GMT on Tuesday, with disagreements over fishing rights the key obstacle to a new trade deal, Brussels sources said.

EU officials said Barnier would then also speak to the European Parliament’s Brexit group, adding that cutting the value of the bloc’s catch in UK waters by around 30% from 2021 would be too high.

The bloc earlier offered a reduction of 15-18%, but the officials said the number was just one piece of the puzzle, with the length of the transition period of beyond Dec.31, as well as how the EU could retaliate if Britain cut its industry out of British fishing waters equally important.

Britain left the EU last January but is only due to quit the bloc’s single market and customs union on Dec.31, when Brexit completes.

The EU, a trading bloc of 450 million consumers, and Britain, the world’s sixth-biggest economy, are trying to put in place before that deadline a new partnership pact to govern ties on everything from trade to transport to energy.

Their current extensive trade exchanges and other types of close links would be badly damaged is there was no agreement, with fallout expected to aggravate the economic damage already wreaked on Britain and the EU by the coronavirus pandemic.