Charges have been laid two years after three mushroom farm workers were killed and two others were seriously hurt at a Langley, B.C., mushroom farm.

Two companies and four people face a total of 27 charges under the Workers Compensation Act and Occupational Health and Safety Regulations.

The Crown says the two companies, A-1 Mushroom Substratum Ltd. and H.V. Truong Ltd. are charged as employers, while the four individuals are charged as either directors or officers of the companies or workplaces.

On Sept. 5, 2008, the workers were overcome by gas in an enclosed space at the mushroom farm and composting plant.

At the peak of the investigation, WorkSafe BC's Donna Freeman said it was one of the most complex investigations the agency had conducted and that 25 investigators were on the file.

Information charging Ha Qua Troung, Vy Tri Trong, Van Thi Truong and Thinh Huu Doan was sworn in a Surrey court on Monday.