The European Parliament has voted overwhelmingly to approve a series of red lines over Brexit - if they're crossed, MEPs say, they will veto the entire deal.
They include the demand that the terms of divorce must be agreed before the two sides can start to talk about trade.
Elena Casas reports from Brussels.
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It's not a resolution that will go down well in Westminster.
MEPs say Britain and the EU can't start talking about trade until they've agreed on a framework for the split - including Britain's exit bill, expected to be around 60 billion euros.
UKIP MEP Nigel Farage called it a ransom demand.
SOT Nigel Farage, UKIP MEP
"You have shown yourselves with this demands to be vindictive, to be nasty, all I can say is thank goodness we're leaving. You're behaving like the mafia, you think we're a hostage, we're not, we're free to go, we're free to go."
Other MEPs don't see it that way - they believe Britain must fulfil it financial commitments, and EU chief negotiator Michel Barnier agrees.
SOT Michel Barnier, EU Brexit negotiator
"We will never seek to punish the United Kingdom, never. We will ask the United Kingdom simply to pay what it has agreed to while a member-state. We need, ladies and gentlemen, Mr Farage, simply to settle the accounts. No more, no less."
MEPs also agreed that Britain can't have a favourable trade deal unless it signs up to all of the EU's environmental and tex evasion rules - a clear warning to the UK not to try and reinvent itself as a tax haven after Brexit.
They also say any transitional deal can't last for more than three years - and must be overseen by the European Court of Justice.
Gianni Pitella leads the socialist bloc in the European Parliament.
SOT Gianni Pitella, chair, Socialists and Democrats
"A country leaving the European Union will never be able to benefit from seceding compared to when it was a member."
The resolution sets the European Parliament and the British government up for a clash - with negotiations set to get underway in earnest in late May or early June.
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