The Construction Forestry Mining Energy Union (CFMEU) charged that 400 workers may have been exposed to asbestos for about one year in the $50-million redevelopment of the Museum of Contemporary Arts building in Sydney.

WorkCover is investigating the claim made by the union that asbestos was in the edifice's sandstone joints, windows and in the lagging of pipes. The museum was originally built in the 1940s as the headquarters of the Maritime Services Board.

Brian Parker, New South Wales (NSW) Secretary of the CFMEU, said the project's contractor, Watpac Constructions, should have known about the risks of asbestos exposure in the redevelopment project. He added the workers should have been informed so they could have put in place more safety precautions such as wearing of face masks.

NSW Planning Minister Brad Hazzard confirmed the presence of asbestos in the mortar of the sandstone building. He asked workers involved to undergo health checks.

However, the Asbestos Disease Foundation said workers would not know for up to 40 years the impact of asbestos exposure on their health. Barry Robson, president of the foundation, pointed out that it only takes one asbestos fibre to create mesothelioma and lung cancer.

To double the size of the building, workers had to knock down parts of the edifice. Mr Parker told ABC that the area should have also been cordoned off and safe removal of the hazardous construction materials should have also taken place.

"Workers have been exposed and possibly their families and possibly the general public as well," Mr Parker warned.

However, WorkCover Authority of NSW acting Chief Executive Officer John Watson dispelled the charge made by the CFMEU. He said the safety watchdog visited the site after the union filed a complaint and it is satisfied that the processes are in place to manage exposure to asbestos.

Although work on the project is on hold due to the Christmas break, the NSW government said the project is proceeding according to timetable and the museum would reopen in May 2012.