Porsche is voluntarily halting the sale of some diesel SUVs in the U.S. and Canada after U.S. regulators accused the brand of using software to cheat on emissions tests.

Porsche said Tuesday that it is halting sales of diesel Cayennes from the 2014-2016 model years until further notice. A Porsche spokesman didn't know how many vehicles were affected.

Porsche's parent, Volkswagen AG, has acknowledged that the software was on smaller diesel engines, mostly used in Volkswagen-brand cars. But the U.S. Environmental Protection Agency said Monday that it also found the software on larger diesel engines in Porsche and Audi SUVs.

Porsche said it was surprised by the news and is cooperating with the EPA.

Audi has not yet said whether it will halt sales of its diesel SUVs.