Ontario's premier is criticizing the federal government over cannabis a day before recreational pot becomes legal, saying police aren't equipped to reliably screen for drug-impaired driving.

Doug Ford says Health Canada has only approved one device to conduct roadside tests for cannabis and it may not give accurate results in the cold.

In a letter to Prime Minister Justin Trudeau, Ford says the federal government must give officers the tools they need to identify drug-impaired drivers.

During a separate speech to the Ontario Provincial Police Association on Tuesday, Ford also said the federal Liberals passed a law to legalize recreational cannabis and left the provinces to clean up "the mess."

The Ontario government has introduced legislation to govern the sale and consumption of cannabis in the province, which is expected to pass this week. Under the legislation, cannabis would be sold online through a government agency starting Wednesday, with private retails stores to follow next year.

The law would also allow people over 19 to smoke marijuana wherever they can smoke cigarettes, with the exception of cars and boats.