A group of foreign labourers and the construction union have closed down a large building site near Canberra's CBD for a rally over 457 visa conditions.

About 60 protesters waving signs gathered outside the site on Mort Street in Braddon for a peaceful protest on Tuesday morning.

Several traffic controllers were organised to help to reduce delays to peak hour traffic heading into the city.

The group is protesting against what it claims is the systematic exploitation of a group of Korean workers hired on 457 visas to paint the apartment building.

The group says it has been bullied into working long hours for below minimum wages, and the union wants the company to back pay each worker.

CFMEU ACT branch secretary Dean Hall says many of the workers were brought to Australia on a 38 hour a week contract but then forced to work more than double that.

"It can be less than 15 dollars an hour without anything like superannuation, sick leave, holiday pay, any of those things. So it's pretty serious exploitation of a class of worker," he said.

"The 457 class of worker which has basically got no rights in a workplace."

The Union says the issue of hiring and then mistreating immigrant workers is far more widespread than the capital.

"Promised things that we accept or take for granted as Australian workers, such as minimum rates of pay and minimum conditions," Mr Hall said.

"When they're out here they're threatened with violence against them, against family members back home. Its almost like a form of slavery."

The company involved denies the allegations but agreed to shut down the construction site for the morning.