TORONTO - GO bus riders can breathe a sigh of relief -- a strike has been averted -- but a walkout by York Region Transit workers began early Monday.

Metrolinx, GO Transit's parent company, said late Sunday that it had reached a tentative agreement with the Amalgamated Transit Union.

Metrolinx said details of the tentative agreement would not be released until the deal is ratified.

However, York Region Transit workers hit the picket lines early Monday, affecting dozens of routes operated by companies contracted to supply service.

They include Miller Transit's 51 routes in Markham, Richmond Hill and Vaughan and 29 operated by First Transit in northern York Region.

About 340 employees represented by Amalgamated Transit Union 1587 are affected by the walkout.

About 220 Viva drivers represented by ATU Local 113 also walked off the job, shuttering service on five express routes.

Union leader Bob Kinnear has said wages are the sticking point and he has called on York Region legislators to step in and help settle the issue.