TORONTO -- Layoff notices have been handed out to 255 workers at the General Motors transmission-making factory in St. Catharines, Ont., as effects spread from a strike that started Sunday at the GM CAMI plant in Ingersoll, Ont.

Unifor 199 chairman Tim McKinnon says at least 255 of the 350 workers at the St. Catharines plant will be laid off starting Monday, likely for at least a week even if the strike is resolved on the weekend.

He says the plant's inventory of transmissions to supply the CAMI factory has built up over the past week because the Ingersoll plant which makes Chevrolet Equinox vehicles has been closed.

GM Canada, meanwhile, says in an update posted Thursday on its website that it has made "production adjustments" at St. Catharines and at two American engine plants in Spring Hill, Tenn., and Flint, Mich., as a result of the strike.

A spokeswoman said in an email no further details would be available.

Earlier Wednesday, parts maker Magna International (TSX:MG) announced it would stop supplying parts to the CAMI plant, a decision it said would affect output at a few of its facilities in Ontario, without being specific.

Unifor Local 88, the union representing 2,500 striking workers at the CAMI plant, says it has invited management to get talks rolling again in hopes of reaching a settlement.

When asked if GM would meet with the union, the spokeswoman sent a copy of GM's statement posted last Sunday which encouraged Unifor to resume negotiations.

Unifor Local 88 says it has been in daily contact with GM since the strike began but no formal negotiations have taken place.

Job security has become more of an issue for the union since GM shifted production of its Terrain SUV from the plant to Mexico earlier this year at a loss of more than 400 jobs.