Canadian National Railway Co (CNR.TO) on Saturday again urged Unifor, the union representing 4,800 of its mechanical, clerical and intermodal staff, to agree to binding arbitration and renewed its threat to lock out those workers on Monday.

Canada's No. 1 railway had called for binding arbitration on Friday when it first announced it was preparing to lock out employees represented by the union.

Unifor, which on Friday called for CN Rail to return to the bargaining table, said on its Twitter feed on Saturday that the railway should negotiate a deal rather than seek arbitration.

With protracted contract talks between CN and Unifor at an impasse, the union had said on Thursday it planned to proceed with a vote to strike.

Unifor made the decision after CN on Wednesday said it would unilaterally alter a labor pact covering staff represented by Unifor if a new accord was not agreed by Feb. 20.

The company reiterated on Saturday that it would deploy a labor disruption contingency plan, with trained management personnel performing the work of Unifor members.