The discovery of a "bong" (a water pipe used for smoking drugs) at an Australian workplace has led to two forklift drivers suspected of smoking marijuana being put on alternate duties.

The Geelong Advertiser newspaper reported building supplier Timbertruss placed the two drivers on alternate duties because of its zero tolerance policy for drugs and alcohol in the workplace.

Its drug testing procedures are being challenged by the Construction, Forestry, Mining & Energy Union (CFMEU) in the Industrial Relations Commission.

Existing tests detect traces of marijuana that may have remained in a person's body for weeks and do not show if a person is drug impaired.

Timbertruss argued it needed a blanket approach because its staff worked with dangerous equipment like forklifts and saws.

However, the CFMEU said there was a risk of people exposed to marijuana through passive smoking being unfairly disciplined.

Commissioner Blair ordered the forklift drivers remain in their new roles until the matter was determined.