EU ministers gathering on Tuesday to adopt a joint negotiating stance on future ties with Britain warned London it must first respect a treaty struck last year that eased the terms of its Brexit. They also stressed that mirroring EU standards will be crucial for British goods to be allowed tariff-free access to the huge European single market.
The stern words highlighted just how fractious EU-UK relations have already become since Britain's departure from the bloc four weeks ago.
The talks to define the future relationship are to start next week and wrap up before the end of this year. Britain, which is to unveil its own negotiating mandate on Thursday, has ruled out extending the negotiating period. The outcome of the talks is uncertain.
We have to first seek a good agreement before giving into timetable pressure, France's EU minister, Amelie de Montchalin, told reporters as she went into the meeting.
The time pressure is immense and the interests are huge, said Dutch Foreign Minister Stef Blok. It's a very complicated treaty. It will be very hard work, a tough road ahead.
The new relationship accord, spanning trade, security, defence and citizens' rights, is meant to kick in from January next year. Failing that, trade would revert to a bare-bones arrangement under WTO rules, causing economic pain on both sides, but especially in Britain.
Britain has nonetheless signalled it is willing to walk away rather than obey EU diktats, saying doing things its own way was the whole point of Brexit.
The EU, however, is insisting Britain retain European norms and keep apace with new ones, fearing that without a level playing field the UK might seek a competitive edge by undercutting tax, environmental and labour standards.
Trust is at a low ebb, with France in particular hardening the EU position and Britain signalling that it may not fully implement the Brexit withdrawal agreement that governs the transition period.
Prime Minister Boris Johnson's spokesman has said British ports are not being readied to carry out checks on goods between Britain and its Northern Ireland territory, despite that being a requirement of the withdrawal agreement.
Irish Foreign Minister Simon Coveney warned that the implementation of agreements that have already been struck are the test of good faith and trust - and without good faith and trust, building a future relationship is not going to be easy.
Germany's EU minister, Michael Roth, was equally blunt. My message is crystal clear to our friends in London: keep your promises, he said.
Under the withdrawal agreement, a protocol on Northern Ireland is to remain in place unless a devolved local government decides otherwise years down the line. Until then, the British territory is to essentially remain under EU single market rules, with a border for goods down the Irish Sea.
But Johnson has repeatedly insisted that there will be no checks on goods going between Britain and Northern Ireland, the agreement notwithstanding.
Last weekend, the Sunday Times quoted an unnamed senior source in his government saying the British negotiating team was looking at ways aimed at not obeying the Northern Ireland protocol.