Purolator has stopped accepting shipments ahead of a strike deadline Wednesday issued by the union representing some of the courier's employees.
Teamsters Canada issued the 72-hour strike notice Sunday after the majority of its more than 8,000 members who work for Purolator voted to reject the company's final offer.
Purolator said in a statement that the company will try its best to deliver shipments already in its network, but delays could occur.
The company said it would not take any new packages until further notice.
The union and the company have been negotiating a new agreement and Teamsters Canada spokesman Stephane Lacroix said a mediation meeting was to take place Tuesday to attempt to avert a strike.
Lacroix said the union won't comment on Purolator's decision to halt new shipments.
The strike deadline is 4:30 p.m. Wednesday.