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
"Thank you for the opportunity to comment on this Jo, and PrintWeek!
Please feel free to get in touch with the Howden Print Team to arrange your own Free of Charge Cyber Micro-Penetration Test to help..."
"I never quite understand the statements such as "achieved such a positive outcome for this well-established business".
The established business unfortunately failed and no longer exists, a..."
"Genuinely sorry to read this."
Up next...

Protocols being strengthened
Software Circle hit by suspected payment fraud

'Precision and reliability'
EBB sets up new publishing wing

Continued investment
Bakers ups BakPac capacity with double Galaxy Packtech install

"Committed to building a stronger Stora Enso"