General Motors is experiencing a number of strikes at several of its plants in North America as well as some of its supplier plants. Most of the strikes surround negations with the UAW over local contracts at individual plants, which would protect worker seniority and job security. On Tuesday, GM ended a strike at its Defiance plant in Ohio by ratifying a new contract with UAW Local 211.

With the latest announcement, GM has now reached agreements with more than a dozen of the 77 UAW locals negotiating contacts. Staff at GM’s Fairfax assembly plant in Kansas are still on strike, while three other local unions continue to negotiate after extending strike deadlines, reports the Detroit Free Press.

The UAW already has a national contract with GM that was signed back in October of last year. The national contract covers such things as wages and benefits. Local contracts, the UAW is now seeking, typically deal with issues specific to a plant, such as work rules and job assignments.

The strikes at the GM plants as well as ongoing strikes at a number of American Axle plants (one of GM’s suppliers) has forced GM to suspend sales of several truck and SUV models including the GMC Yukon, Denali, Sierra heavy-duty regular and extended cab, its commercial-duty pickup and variants of Chevrolet trucks and Tahoes.