However, the company is assuring customers that "service will not be affected."

"Porter Aviation Holdings Inc. has the internal resources to maintain a safe and efficient operation by using other fully-trained staff and management to fill these roles," said spokesman Brad Cicero in a statement.

Mary Stalteri, representative of the Canadian Office and Professional Employees Union, Local 343, confirmed Porter is "preparing to use replacement workers" in the event of a walkout.

The 22 unionized employees will be in a legal strike position at 12:01 a.m. Thursday.

Union representatives and management are scheduled to meet Wednesday morning in a final effort to resolve this impasse before the deadline.

Stalteri said the workers presently earn "less than the industry average" and are seeking a wage increase.

"We sincerely hope to be able to prevent a strike and unnecessary inconvenience to the travelling public," she said.

In its statement, Porter Aviation Holdings said: "We're disappointed that the union is trying to intimidate customers by suggesting flights will be disrupted if there is a strike or lockout."

The company also denied the union's claim of substandard wages.

"Porter ... benchmarks it wages and benefits against both aviation and non-aviation companies to ensure we are competitive and will continue to do so. We also paid profit sharing to every team member for 2011's results."