A federal mediator is stepping in to try to sort out the postal dispute before end of day Sunday. This, after the union served 72-hour strike notice Thursday after months of failed negotiations. Labour minister MaryAnn Mihychuk says sometimes when negotiations drag on the two sides fall into a rut and things need to be shaken up. Still, she said Canadians need to be prepared for a potential wok stoppage come Monday. The last time there was a strike it began with a series of rotating walkouts before Canada Post invoked a lockout of workers. Back-to-work legislation was eventually introduced, but the government says that won’t happen this time.