WASHINGTON — Federal safety regulators are investigating a few reports of gas pedals becoming trapped by floor mats in 2010 Ford Fusions and Mercury Milans.

The National Highway Traffic Safety Administration opened a preliminary investigation Friday after receiving three such complaints involving unsecured all-weather floor mats. There are no reports of crashes or injuries.

A Ford spokesman, Said Deep, said the problem was due to drivers stacking all-weather mats on top of floor mats that come with the vehicle. Ford's all-weather mats have warnings advising customers not to pile them and to secure them properly to the floor, he said.

In a consumer advisory Tuesday, NHTSA said the problem was most likely to occur when a driver pressed on the pedal while merging or passing in traffic. The safety agency also warned Fusion and Milan owners not to stack mats.