Amazon’s self-driving vehicle unit is coming under increased scrutiny, as the National Highway Traffic Safety Administration has announced that it is stepping up an inquiry into how Zoox certified its autonomous vehicle for use on public roads.

The company, which was purchased by Amazon in 2020, announced last summer that it was applying for a robotaxi license in California after claiming that it had created a vehicle that complied with all federal requirements.

“Self-certification of a purpose-built vehicle that does not rely on traditional human driver controls is a historic milestone in the autonomous vehicle industry,” Dr. Mark Rosekind, Zoox’s chief safety innovation officer, said in July. “Safety is foundational to everything we do at Zoox, and this achievement is a testament to this mindset.”

Read: Amazon-Owned Zoox Applies For Robotaxi License In California

 Amazon’s Zoox Faces Inquiry Over Autonomous Vehicle Certification For Public Roads

On September 6, however, NHTSA issued a Special Order, demanding that Zoox answer questions and provide information about how it self-certified that its vehicles met federal regulations – a process other autonomous vehicle manufacturers are also entitled to complete.

Zoox responded the following day, but NHTSA said that, as it continues to evaluate the responses, it has determined that “further examination is necessary into the process and technical data on which Zoox relies when certifying vehicles.”

In particular, the federal agency is concerned with “the extent to which Zoox’s certification basis depended upon unilaterally developed test procedures or determinations that certain standards were inapplicable due to the unique configuration of the vehicle.”

For its part, Zoox claims that its vehicle, a ground-up autonomous pod with no steering wheel and seats that face one-another, meets all requirements.

Its self-certification tests “have met or exceeded applicable (federal) performance requirements. We are committed to working closely with NHTSA on the questions they have, and we remain confident in our self-certification process and data,” Christopher Nalevanko, Zoox’s general counsel, told Reuters.

Whether Zoox will continue to be able to use its autonomous vehicle to ferry its employees from one of its buildings to the other, a short trip that takes it on public roads, remains to be seen.

 Amazon’s Zoox Faces Inquiry Over Autonomous Vehicle Certification For Public Roads