The UK is struggling to keep the Working Time Directive opt-out clause it thought it had secured with concessions on agency workers, according to a key figure.
MEPs are expected to pass the Agency Workers Directive in its current form next week, giving temporary staff equal rights to permanent employees after 12 weeks with an organisation.
UK employers originally campaigned for a much longer time lag before the rights kicked in.
However, the UK had come under increasing pressure to ditch its opt-out from the Working Time Directive's 48-hour working week limit. It was widely accepted that the Agency Workers Deal had secured the Working Time opt-out - but now that appears to be under threat.
David Yeandle, head of employment policy at manufacturers' group and government lobbying body the EEF, told Personnel Today: "While an approved draft of the Agency Workers Directive has been put forward by ministers, the Working Time Directive is a very different scenario. It is taking much longer and proving much more controversial."
He said that MEPs were not party to the deal made between member states, and could yet insist the UK signs a timetable to end its opt-out.
"There is a real possibility that there will be enough of a majority in Parliament to block the progress of the directive," Yeandle added.
The Recruitment and Employment Confederation highlighted the significance of next week's vote on the Agency Workers Directive.
Director of external relations Tom Hadley said: "The strong likelihood is that the European Parliament will approve the text that was agreed by the EU Council last June.
"The vote is extremely significant as this will mark the conclusion of this directive being debated, disparaged, defended, blocked and finally accepted as a workable compromise after more than seven years of intense activity in Brussels."