MONTREAL -- The Teamsters union is warning of a potential strike or lockout at CN Rail starting on Oct. 28.

The Teamsters Canada Rail Conference said in a statement Monday that its offer to continue a conciliation effort, which ended Oct. 7, has been rejected.

The union represents some 3,300 conductors, trainmen, yardmen and traffic co-ordinators at CN (TSX:CNR).

Spokesman Roland Hackl says the union is "extremely disappointed" by CN's refusal to extend mediation to forge a contract to replace one that expired July 22.

A CN spokesman says the company is optimistic it can reach a settlement with the union "to avoid labour disruption in Canada," adding the earliest date for a strike or lockout is one minute after midnight on Oct. 29.

Mark Hallman said in an email Tuesday that the two sides are scheduled to resume collective bargaining on Oct. 21, with the help of federally appointed mediators.

He said those mediators had acted as conciliators during the conciliation process that ended Oct. 7.

Hackl, the union spokesman, said in his statement that the railway is using an old tactic of "pointing a gun to its workers' heads to force them to make concessions."

Hackl said the concessions being sought would see CN workers work longer hours with less rest time in between trips.

He said this "flies in the face of scientific research on fatigue management" and seems to contradict CN CEO Claude Mongeau`s July statement that railways had to make safety their "number one priority."

"CN's managers have to walk the walk and talk the talk; they have to understand that people are not machines and that you should never place profits before people," added the union statement.

Hallman said CN does not comment on on-going labour negotiations as a matter of policy.

But he added: "CN stresses that none of its bargaining proposals would in any way compromise the health and safety of TCRC members. Indeed, it is our opinion that CN's proposals would positively affect the health and safety of our employees."