Steel sections of Wembley's roof need to be erected by October

Multiplex is facing the risk that the stadium - already overbudget - would not be ready by January, which would incur financial penalties for the firm.

The National Joint Council (NJC) for engineering unions and workers has now suspended its site agreement at Wembley.

The NJC has called for a report into the Multiplex bonus scheme.

Pressure to complete

The Stadium needs to be ready by the FA Cup Final

Steel workers who take the extra pay - reported to be as much as �8,000 ($14,547) - will not be allowed to participate in the NJC's disputes procedure, said the NJC, which represents construction workers and trade unions.

It claims that Multiplex's "incentive scheme" contravenes the construction industry's "blue book" agreement, which seeks to define best practice.

The incentive scheme - announced on Monday - seems likely to have been prompted by the need to have the stadium's steel roof finished by October.

Problems with an earlier steel contractor are thought to have contributed to cost overruns and delays.

Further delays could jeopardise the stadium's chances of hosting the FA Cup Final in May 2006.

Multiplex faces penalties of �3m a month if the stadium is not complete by the 31 January handover date.