A group of cannabis testing labs in Michigan claims that a large amount of marijuana on retail store shelves is rife with mold and yeast.

Members of the Michigan Coalition of Independent Cannabis Testing Laboratories have tested licensed cannabis in the state’s stores and found such contamination, the Detroit Free Press reported.

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The revelation follows state regulators discontinuing a testing method it claims resulted in false negatives – or allowed contaminated marijuana to pass testing.

However, the Michigan Cannabis Industry Association disputes the lab group’s findings, saying the state’s move to halt the testing method was done for safety reasons and was not based on evidence of tainted marijuana.

“From our perspective, there has not been any indication there is contaminated product in the system,” Robin Schneider, the executive director of the association, told the Free Press.

Shady practices by marijuana testing labs and an overall lack of standards is an ongoing problem for the industry.