TORONTO - Metrolinx says it's monitoring rails in the Greater Toronto and Hamilton Area due to a heat warning from Environment Canada.

Metrolinx says intense heat can cause safety issues that could require temporary slow orders for trains on its GO Transit and UP Express services.

Temperatures for Tuesday and Wednesday are expected to be near or hotter than 31 Celsius.

The transit agency says sustained high temperatures above 30 degrees can cause what it calls "sun kinks" in steel rails.

It says these bends in the rail can be a safety issue if trains pass over them too quickly.