According to USA Today, Audi has a bit a problem right now. Apparently, it doesn't have enough cars to sell, specifically three of its top sellers, the A3, A4, and A5. Could this be a reason why Volkswagen Group just announced a 16 percent US sales decline last month? Very likely, yes. Welcome to supply issues. But what's causing them?

Audi spokesman confirmed the model shortage to the news site and blamed certification by US environmental regulators for the delays. Turns out these delays are linked to the automaker's failure to receive timely approval from European regulators following newly imposed Worldwide Harmonized Light Vehicle Test Procedure (WLTP) standards.

Audi isn't the only automaker to be experiencing certification difficulties, but this really couldn't come at a worse time. Audi, BMW, and Mercedes-Benz have for the past several years been competing for the top luxury brand sales spot in the US and this shortage essentially knocked Audi out of the running. At the moment, the final year-end tally between BMW and Mercedes-Benz is too close to call.

The Audi spokesman added the vehicle shortages won't be rectified until later this or next month. But the WLTP standards arose mainly due to the Dieselgate fallout. Ironically, the main cause of VW Group's luxury brand US vehicle shortage is something of its own doing.

Aside from the three vehicles listed above, no other Audi model is in short supply, at least not yet. Unlike BMW and Mercedes-Benz, Audi does not have a US-based production plant, so even once WLTP issues are sorted, there's still the issue of transportation time. Obviously this is a big deal and Audi is fully aware that it's continuing to lose income. But then again, these rigorous emissions standards may not even exist if it weren't for VW Group's past criminal acts.