Ireland’s European commissioner for agricultural, Phil Hogan, has warned his country would prevent the UK’s Brexit negotiations from progressing on to trade if it doesn’t resolve the border issue.

Hogan told The Observer that Ireland would “continue to play tough until the end” and potentially veto trade talks until the UK made certain guarantees over its border.

The Irish government wants guarantees that there would be no hard border between the Republic of Ireland and Northern Ireland once the UK leaves the European Union.

Hogan’s comments present a new challenge for prime minister Theresa May, who has days left to move the UK’s talks with the EU on from the opening issues of citizens’ rights, the Irish border, and the Brexit bill, to trade. EU officials will want to see sufficient progress on all three before permitting negotiations to move to trade.

Here’s what Hogan said:

“If the UK or Northern Ireland remained in the EU customs union, or better still the single market, there would be no border issue. That’s a very simple fact. I continue to be amazed at the blind faith that some in London place in theoretical future free trade agreements. First, the best possible FTA with the EU will fall far short of the benefits of being in the single market. This fact is simply not understood in the UK. Most real costs to cross-border business today are not tariffs – they are about standards, about customs procedures, about red tape. These are solved by the single market, but not in an FTA.”