There is no need to buy back credit in the following situations because your pension benefits continue to accumulate seamlessly during your absence:

A legal strike
Your pension credit is not affected during a legal strike or lockout. Your employer reports a loss of salary, but not your absence. This means you do not lose credit during a legal strike. If a strike occurs in one of your "best-five" years, you or your federation can make up the loss in salary.

A deferred salary leave
Your employer continues to deduct pension contributions from your pay while you are on a deferred salary leave, sometimes known as an "x over y" plan.