Electric vehicle startup Nikola announced Sunday its founder and executive chairman, Trevor Milton, has voluntarily stepped down. The sudden chain comes amid controversy surrounding the integrity of information reported to the public and investors.

Nikola says current board member Stephen Girsky will take over as executive chairman. Girsky is the former vice chairman of General Motors following its emergence from bankruptcy in July 2009. Girsky is also a Managing Partner of VectoIQ, LLC, an independent consultant firm.

The shuffle at the top of Nikola comes amid investigations into the company’s claims surrounding its technology and capability. Investment company Hindenburg Research has accused Nikola of being an “intricate fraud” in a recent report, saying the company falsely claimed it has proprietary technology.

Hindenburg Research’s report came after Nikola and General Motors announced a partnership worth $2.5 billion in which GM will produce Nikola’s Badger pickup with its platform and Ultium battery technology. The deal raised significant questions surrounding Nikola’s previous claims that it had proprietary battery technology.

Nikola refutes the report, saying Hindenburg was intentionally attempting to manipulate the company’s share price.

The Department of Justice and Securities and Exchange Commission has launched a probe into Nikola following the report. At this time there is no formal investigation into the matter, according to the Financial Times

Nikola’s deal with GM is expected to close on Sept. 30th. GM has stated it fully vetted the startup prior to agreeing to the deal.