Tensions between the Olympic Delivery Authority (ODA) and trade unions deepened this week, appearing to jeopardise the 2012 construction commitments on industry best practice.

In July 2006 the ODA promised to establish agreements with unions covering workers’ conditions on the project. But Building understands the ODA is now offering only one agreement, which unions will reject as it opens the door for the use of agency labour.

The ODA is in the process of drawing up a memorandum of agreement that one senior union source said unions would refuse to sign. He said: “Signing would mean signing away the workers’ rights. We told them no.”

The unions want the ODA to guarantee 100% direct employment. They say other arrangements would leave workers open to exploitation. The ODA says implementing this is impossible. An ODA spokesperson said: “We’re having positive discussions with the unions. We have agreed most items and expect to resolve outstanding issues soon.”

The two groups have been deadlocked over the issue since December, despite a series of meetings. The gravity of the dispute has led David Higgins, the ODA’s head, to become involved. Building understands that the unions are due to meet him next week.

When the construction commitments were drawn up it was envisaged that the unions, the ODA and employers would work together over best-practice working conditions. The ODA compared it to BAA’s Heathrow T5 project, where workers can earn up to £55,000 for increased productivity.