The battle between Lyft and Uber is heating up — and this time they’ve taken it off the road and into the courtroom.

Lyft, which has been trying to expand oversees, brought a lawsuit against a former executive who allegedly took proprietary information on Lyft’s international plans with him to his new job at Uber, according to documents filed with the California courts Wednesday.

Travis VanderZanden previously served as chief operating officer at Lyft and left the ride-sharing company in August. He joined Uber last month as the vice president of international growth.

Lyft is suing VanderZaden for breach of contract and said he carried “Lyft’s most sensitive documents” with him, which allegedly includes financial information, strategic planning, customer lists and international growth plans. Lyft said in the complaint that he transferred the documents to his personal Dropbox account in the weeks and months leading to his departure.

VanderZaden took to Twitter to respond to the lawsuit, saying that he didn’t take any confidential data to Uber.

VanderZaden and Steve Schnell, another former Lyft executive, resigned from their roles at the company following disagreements with co-founders Logan Green and John Zimmer concerning how the company operates, reported Bloomberg News. Schnell also joined Uber to help with its international expansion.

“We are seeking the assurances we need and are entitled to in order to responsibly run our business,” a Lyft spokeswoman said via e-mail. “We are disappointed to have to take this step, but this unusual situation has left us no choice but to take the necessary legal action to protect our confidential information.”

A representative for Uber did not immediately respond for comment.