Workers are demanding compensation for travelling time

They say it can take up to 90 minutes to reach Terminal 5 due to transport arrangements and heightened security.

Amicus had warned it was planning to ballot 500 union members, working for 14 contracting firms, over action.

On Friday night airport operator BAA and the union said talks would be held on Thursday to try and resolve issues.

'Secure site'

"However, we have not called off our threat of potential strike action," said Amicus' regional officer Frank Westerman.

"I will be holding two meetings on site with workers next Tuesday, before the talks with BAA."

Amicus wants the workers reimbursed �25 a day for additional travelling time.

It claims the stepping up of security checks over the past two years, plus an increase in workers at the site, has increased congestion.

Last week Heathrow's operator BAA had said the issues were "understood at the outset".

BAA, which hopes the new terminal will be operational by 2008, said issues about keeping T5 "a secure construction site at the western end of the airport" were recognised in negotiations that took place with Amicus in December 2003.