Fresh labour problems look set to trouble the £220m Royal Opera House refurbishment after an inter-union dispute broke out over a plate of beans.

Site workers employed by Alendale Construction stopped work last week and have threatened further industrial action after a colleague accused of throwing the beans at an electrician in the site canteen was removed.

AEEU electricians had earlier stopped work and called for the sacking of the man, who guided crane drivers, claiming he was a risk to health and safety.

Alendale's workers are members of construction union UCATT, whose officials were called in this week in a bid to defuse the confrontation.

UCATT official Jerry Swain said: "The unrest among workers with electricians on this project is unique in my experience. I think the attitude of the electricians' union site representatives has been regrettable to say the least. They have acted as judge and jury and have jeopardised the living of one of our members." The man involved claimed he was racially abused by the electrician but withdrew the accusation when the two men shook hands and agreed to drop the matter.

A site worker said: "We can cause as many problems as the sparks. You cannot have 200 sparks ganging up to sack one fella. Who's running the job, Schal or the electricians?" Alendale refused to comment, but construction manager Schal said: "Site operatives have expressed concerns for each of the individuals involved. Because of this, the issue is being resolved by Schal, the trade contractors concerned and union officials."