Experts believe that agency workers could be granted equal rights at an even earlier stage as the agreement between the government, the CBI and the TUC are yet to be rubber stamped by European employment ministers.
The European Parliament will then decide whether to give the UK government the go-ahead to implement the deal into UK law as part of the Agency Workers Directive.
David Yeandle, deputy director of employment policy at manufacturers' organisation the EEF, warned that the government faced a massive challenge to convince ministers and EU officials to stick to the 12-week limit.
He warned that employers are a long way from the end of the road with this deal and there are still a number of hurdles to clear and officials might be unhappy with its wording and take a much stronger line.
Yeandle conceded that the 12-week threshold was better than the six weeks proposed in the current directive, but said it was still a long way away from what employers had originally wanted. The CBI has called the deal the least worst outcome available.