Deputy general secretary Tony Burke said the union was "disappointed" that MEPs had approved an amendment that meant agency workers would only be guaranteed pay on a par with permanent workers after six weeks in a company.
The exemption will operate for the first five years after the directive becomes law and only applies to the UK and Ireland.
The GPMU has argued that temps should get equal rights from day one, and Burke said the six-week "loophole" would allow "unscrupulous companies and agencies to continue to exploit agency workers". "Once again we will see the UK lagging behind the rest of Europe," he added.
Have your say in the Printweek Poll
Related stories
Latest comments
"15 x members? Why don't they throw their lot in with the Strategic Mailing Partnership (SMP) and get a louder voice?"
"Some forty plus years ago I was at a "sales" training seminar and got chatting to the trainer after the session had finished.
In that conversation he told me about another seminar he had..."
Up next...

New owner is 'patient, committed investor'
Shareholders green light Royal Mail takeover

Two other tenders also available
House of Commons contingency printing tender live

Wide-format's gala expo
Visionaries welcome

Global Print Expo