It says that EU standards should serve as "a reference point" in any future trade deal.
Meanwhile, UK ministers will also meet at No 10 to discuss the government's opening stance for negotiations.
The final agreement is due to be published online and presented in Parliament on Thursday.
The EU's mandate - a 46-page document - says that its "envisaged agreement should uphold common high standards, and corresponding high standards over time with Union standards as a reference point".
It says this should apply "in the areas of state aid, competition, state-owned enterprises, social and employment standards, environmental standards, climate change, relevant tax matters and other regulatory measures and practices in these areas".
BBC Brussels correspondent Adam Fleming said: "This is the blueprint that [EU chief negotiator] Michel Barnier will follow in the negotiations.
"We've learnt from experience these documents are very important because the EU will only accept a final outcome that is pretty similar to this starting point."
It is "the roadmap for all the rows we're going to have over the next few months", our correspondent added.
Nathalie Loiseau, an MEP for French President Emmanuel Macron's La République En Marche! party, said the bloc wanted clarity about what the UK wanted to achieve in trade talks.
"If you would like to lower the standards [in areas such as food, farming], there would be mechanism to protect us from any sort of unfair competition," she told BBC Radio 4's Today programme.
"But the question I would like to ask is: what sort of discussion will your government have with other trade partners? Will you abide to American standards in terms of consumer protection for instance? This is still unclear to me."
It is expected that ministers in the UK will commit to seeking a Canada-style agreement with zero tariffs, a proposal Mr Johnson and his Europe adviser David Frost have set out in speeches in recent weeks.
But the push for a Canada-style deal could set up a clash with the EU after its chief negotiator Mr Barnier ruled out such an agreement.
Mr Barnier has previously said the UK is too close in proximity to be permitted to compete with the other 27 member states on such terms.
And Ms Loiseau said that "to my knowledge the UK is not Canada", adding that the EU-UK relationship is "very different" from the one with Canada.
'Tough road ahead'
Arriving at the meeting of the General Affairs Council in Brussels, Croatia's European Affairs minister Andreja Metelko-Zgombic said the EU would be willing to offer a "substantial" and "ambitious" partnership in trade talks.
But Dutch foreign minister Stef Blok warned it will be "very hard work" and a "tough road ahead".
And Irish Deputy Prime Minister Simon Coveney said the prospect for a UK-EU free trade agreement will be "damaged significantly" if Britain did not build the infrastructure required for checks on goods crossing the Irish Sea.
The offer the EU was making to the UK was "generous and fair", he said.
BBC assistant political editor Norman Smith said the EU's proposals "have been given a decidedly cool response from government sources", who say the UK's priority is about control.
He said the "mood music" from Number 10 was that the prime minister "is quite prepared to walk away" and use World Trade Organization (WTO) rules.
When countries do not have free-trade agreements they use these terms. Under the WTO rules, each country sets tariffs - or taxes - on goods entering.
