A worker at City’s under-construction £120m Etihad Campus says labourers have been ordered to take off their United shirts.

The man, who does not want to be named, claims bosses at the 80-acre site have told all of those who work there that football shirts are banned and that anyone found breaking the rule runs the risk of being sacked.

He said things came to a head at the Ashton New Road development, which will become City’s new training ground, earlier this week when two Reds-supporting workers were told to take off their United shirts.

But BAM, the construction firm building the complex deny that workers were discriminated against because the shirts they were wearing were those of the Blues’ fiercest rivals.

The worker said: “Because the weather has been so nice a lot of the lads have been wearing football shirts. Some of those have been United shirts but on Tuesday two lads wearing United shirts were told to cover them up or get off the site.

“They asked why and were told that there was a no-football shirt policy. They said it was in the rules but it’s the first we’ve heard of it.”

The worker added: “We see a silver Land Rover giving people tours of the site and I think that the club may have been embarrassed by it.”

He also claimed that site bosses were carrying out spot inspections at areas of the site where concrete is poured in a bid to stop workers of a Red persuasion burying United paraphernalia in the foundations. The claim is denied by BAM.

The worker said: “It’s annoying a lot of the lads working there and you are now starting to see bit of ‘MUFC’ graffiti about the place.

“They are annoyed because builders always wear old football shirts. The site is in Manchester and so people are going to wear United shirts.”

Ian Fleming, from BAM Construction, said: “BAM took the decision from the start of this project to ban all football shirts on site to avoid any partisan alliances being brought into the work place. This policy is reinforced in all sub-contractors terms of reference. We are treating any football shirts, no matter what the team, in the same way. We may have missed some but are striving to enforce the policy site wide. Strict building regulations are laid down for elements of the construction process one of which is for a local building control officer to inspect the quality of a structural concrete pour which includes checking the foundations.”

City hope to move from their Carrington base to the new complex, which will be connected to the Etihad Stadium by a bridge, in time for the 2014-15 season.

It includes 16 full-size football pitches, a Fifa regulation indoor pitch and a training, medical and operational facility. A sixth-form college and sports centre for community use is also being built on the site which was once the home of the Clayton Aniline Company.