A project of Google-parent Alphabet has filed a suit against Uber, after a botched email exchange revealed "striking resemblance" between the companies' self-driving car designs.

Engineers at Google's self-driving car company, Waymo, were "apparently inadvertently" copied on an email from a company providing components for Uber's self-driving car project that allegedly revealed drawings of Uber's technology, according to a lawsuit filed in San Francisco court on Thursday.

The drawings of the 3-D sensors contained Alphabet's trade secrets, the lawsuit claims. The suit also alleges that a former Google employee "downloaded more than 14,000 highly confidential and proprietary files shortly before his resignation."

The engineer, Anthony Levandowski, took "extraordinary efforts to raid Waymo's design server and then conceal his activities," the suit alleges. Levandowski left Google to launch a self-driving truck company called Otto, which went own to be acquired by Uber.

"We take the allegations made against Otto and Uber employees seriously and we will review this matter carefully," an Uber spokeswoman told CNBC.

It all comes at a tough time for ride-hailing technology company Uber, which is facing fallout amid complaints about its company culture.

The two companies once had close ties. Alphabet's venture capital arm invested in Uber, according to Crunchbase, and Alphabet executive David Drummond once sat on Uber's board.

But Drummond stepped down in August "given the overlap between the two companies," amid reports that Drummond had been shut out of board meetings. Uber revealed it had bought Otto that same month.

"Misappropriating this technology is akin to stealing a secret recipe from a beverage company," Alphabet said in a statement.