UNION legal experts are considering plans to turn the picket line at Wembley National Stadium into an official strike.
Lawyers at general union GMB and electrical and engineering union Amicus are poring over employment laws to see if the action can be made official.
GMB regional official Kelly Rogers said: 'Our solicitors are considering ways of making the strike official and we expect a decision this week.'
Around 150 steel workers were manning the picket line as Construction News went to press.
The men started their unofficial protest at the site gates after having their contracts terminated by Hollandia two weeks ago following a dispute over working hours.
Picket Barry Breech said: 'We have been talking with the GMB legal team and we are confident this strike will be made official this week.'
Another said: 'There is no way this is going to fragment.There is too much support and too much sympathy and it looks like only a matter of days before the strike becomes official.'
But a source close to Amicus said: 'Our people are looking at how it could be made official but there are a lot of problems.
'You have to have a ballot and to do that you need to notify your employer.These men haven't got an employer, so whatever they do would be classed as secondary action and would be illegal.'
The steel workers were originally employed by Cleveland Bridge but transferred to Hollandia in July after the Dutch firm was brought in to replace Cleveland by main contractor Multiplex.
Last Thursday 21 white-collar workers from Cleveland Bridge were also given two hours to get off the site.
A Cleveland spokeswoman said most of the engineers, who had remained on site to help with the transfer of work to Hollandia, had now gone back to the firm's Darlington headquarters.
A Multiplex spokesman said: 'Half of them were scheduled to leave last week and given the progress of the project, the others were no longer required.'
The spokesman added that 80 new steel erectors were currently on site and that they were confident of 'having a 150strong team soon' A source close to the site said: 'Looking back, you can see how this all blew up.
'Hollandia came in and took the men on, then it rained all month and the cranes were stopped after an accident.
'That meant the Dutch were paying 200 people a grand a week for doing not a lot.
'Then the lads started kicking off over working hours and Hollandia just showed them the door.'