BEIJING — A Chinese court on Saturday ordered the retrial of a Canadian man on a drug-smuggling charge after siding with prosecutors who argued that his original 15-year prison sentence for his conviction had been too light.

The decision threatened to create another source of contention between two countries whose relations have deteriorated rapidly this month after a string of arrests.

The Canadian, Robert Lloyd Schellenberg, was arrested in 2014 and tried and sentenced in obscurity. But he is likely to became a focus of attention in Canada after the court in Dalian, a port city in northeast China, responded to his appeal against a sentence he received last month by siding with prosecutors and opening the possibility of an even harsher sentence.

If the prosecutors prevail in the retrial, Mr. Schellenberg could be sentenced to a longer term, or even the death penalty, at a time when China and Canada are locked in an escalating dispute that began with the arrest in Vancouver of a prominent Chinese technology executive.