MONTREAL - The union representing CN Rail mechanics and electricians says benefits and the contracting out of repair and overhaul work are key issues as negotiations begin on a new collective agreement.

Unifor National president Jerry Dias says workers are frustrated that work they have historically done is being contracted out.

The union representing 2,100 workers across the country who repair and maintain railway cars is also seeking improved benefits and wages from the profitable Montreal-based railway.

The union says the two sides exchanged proposals and have booked several dates to begin negotiations to replace a collective agreement that expires Dec. 31.

Unifor is Canada's largest private sector union, representing 315,000 workers.