Britain fiercely defends the opt-out as part of it liberal approach to the economy.
After a change of government in France last year, Paris dropped its demand that the opt-outs should be scrapped and in December all ministers agreed in principle to leave it be.
But in return, they asked Britain to make concessions in a review of the law on the rights of the EU's 8 million temporary agency workers. Between 600,000 and 1.4 million of those are in Britain, forming 2.6 to 5.1 percent of the workforce.
The deal is likely to satisfy countries focused on setting minimum social standards, because it gives temporary workers equal rights to full-time staff from day one, unless trade unions and employers agree otherwise.
"Today's agreement between social partners will facilitate the negotiations in the (EU) Council," EU Labour Commissioner Vladimir Spidla said in a statement. "I am confident that the Slovenian Presidency will bring about an agreement at the next Employment Council."
The umbrella Trades Union Congress welcomed the move to give agency staff more rights in the workplace, after a six year offensive by unions to win concessions.
But business has long resisted giving temporary workers more rights and lobby groups argued the changes could result in fewer jobs for agency staff.
"This is a disastrous deal for small businesses, which rely on the flexibility provided by agency workers," said Tina Sommer, EU and International Affairs Chair at the Federation of Small Businesses.
She said the deal would boost the cost of temporary workers making them unattractive to small businesses.
The Confederation of British Industry - the nation's biggest business lobby group which helped broker the deal - said half of agency assignments last less than 12 weeks and will therefore be unaffected.
"There has been a major risk of damaging legislation coming from Brussels, and the CBI has judged that the government's proposals represent the least worst outcome available for British business," said John Cridland, deputy director general at the CBI. Sick pay and pensions are excluded from the deal.
