General Motors Canada breached its contract when it reduced the health care and life insurance benefits for some of its retired workers, an Ontario court ruled Wednesday.

In a 27-page decision, Ontario Superior Justice Edward Belobaba said GM Canada was "not contractually entitled" to make changes to the benefits of salaried retirees.

In some cases, the long-time retirees saw their basic life insurance benefit cut from more than $100,000 to $20,000.

However, the court ruled the automaker was within its rights to reduce or eliminate some of the additional benefits enjoyed by its executive retirees.

The decision comes after a class action lawsuit was launched against GM Canada in 2010.

The case was on behalf of more than 3,297 retirees and their families including 67 executive retirees.