A letter from the U.S. Securities and Exchange Commission (SEC) produced by a short seller shows that the regulator has opened a probe into electric vehicle maker Workhorse Group Inc.

In its letter dated June 30, the SEC disclosed that its enforcement division had been investigating Workhorse and that the probe is “still active”.

A copy of the letter has been published on Fuzzy Panda Research’s website.

In June, Workhorse had challenged a decision by the U.S. Postal Service to award a multibillion-dollar 10-year contract to Oshkosh Defense to manufacture a new generation of postal delivery vehicles.

Fuzzy Panda Research describes itself as being a short seller on its website. It did not respond to a requests for comments on the letter.