WASHINGTON – The Senate Finance Committee opened a probe Tuesday into Volkswagen’s use of a federal tax credit intended for fuel-efficient cars as the company’s emissions-rigging scandal widened.

Sens. Orrin Hatch, R-Utah, and Ron Wyden, D-Ore. said in a letter to Volkswagen that more than $50 million in tax subsidies may have gone to VW owners under false pretenses. Hatch chairs the Finance panel and Wyden is its senior Democrat. Volkswagen’s use of “defeat devices” in diesel passenger cars raises the question of whether the automaker “made false representations to the U.S. government” in certifying that the VW Jetta and other models met emissions standards needed to claim the $1,300-per-veheicle tax credit, the senators said. The Associated Press obtained a copy of the letter, which was sent to VW late Tuesday.

The vehicles in which Volkswagen installed the defeat devices “included those that the company certified as qualifying for the advanced lean-burn technology motor vehicle credit,” Hatch and Wyden said.

The letter asks the company to respond by Oct. 30.

The Senate Finance probe comes as the House and Energy Committee has scheduled a hearing Thursday on the emission-rigging scandal. The hearing is the first since VW admitted that it installed defeat devices in nearly 500,000 diesel vehicles in the U.S. that emitted far more exhaust pollution than was legal. The German automaker has confirmed that it installed the devices on as many as 11 million vehicles worldwide from model years 2009 through 2015.