The Health Canada agency said in a release mold was found in the sterile manufacturing area at the Sanofi Pasteur company's Toronto plant and production was halted.
"In light of the manufacturing problems at the Toronto plant, there may be a global impact on the supply of ImmuCyst," the agency said. "Health Canada will continue to consult with its international regulatory counterparts, including the U.S. Food and Drug Administration."
The federal regulator said before any of the existing ImmunoCyst inventory is released, samples from all production batches will be tested.
There is an alternate bladder cancer drug available in Canada, but the agency didn't name it.
In mid-June, Sanofi Pasteur voluntarily recalled all of its Bacille Calmette-Guérin tuberculosis vaccine produced in the same Toronto plant.
The pharmaceutical building experienced a small flood last October which is the likely source for mold, the company said.