Quinn Emanuel Urquhart & Sullivan ended its relationship with Uber due to fixed fee arrangements with the company that were described as having been at rates "that are not financially viable" for the firm, according to court filings.

The details behind the firm's decision to end its lawyer-client relationship were revealed in a recently filed document in the ongoing legal battle between the ride-hailing giant and Alphabet self-drive venture Waymo.

In a 20 July filing from Uber, it emerged that Quinn Emanuel, which now represents Waymo in the dispute over driverless car technology, emailed a number of top lawyers in Uber's legal department, including current chief legal officer Salle Yoo, to cut off the relationship.

The email from Quinn Emanuel partner Stephen Swedlow, dated 23 September 2016, noted that, since the firm entered into Uber's preferred counsel programme with fixed fee arrangements, the cases and tasks it has been hired for have "been at rates that are not financially viable" for the firm.

"As we have discussed many times, if [Quinn Emanuel] was also getting the cases with larger amounts in dispute involving more significant budgets, the smaller tasks on smaller cases would be part of the overall relationship," Swedlow, who is co-managing partner of the firm's Chicago office, wrote in the email. "But we have not gotten any of the larger disputes for Uber under the preferred counsel programme."

Quinn Emanuel's relationship with Uber spanned four and a half years, according to the email, and included representing the company in a dispute with Yellow Cab in Chicago, a class action suit that alleged Uber unlawfully took a cut of driver gratuities, and a suit claiming the ride-hailing service charges unfair ride cancellation fees.

While acknowledging it was a difficult decision for the firm, Swedlow added: "It is no longer feasible to serve the role we have been relegated to in the context of representing Uber."

Quinn Emanuel and Uber both declined to comment on the July filing or their relationship.

Uber's reason for seeking Swedlow's email can be found in a June 21 filing in which the company moved to compel production of a number of documents by Waymo, including communications that would establish when the possibility of legal action against Uber or former Waymo manager Anthony Levandowski was first discussed with Quinn Emanuel.

"With no prior notice, Quinn Emanuel fired Uber as a client one month before Waymo filed its arbitration action against
 Mr Levandowski," the filing stated. "If Quinn fired Uber as a client knowing that Mr Levandowski or Uber was going to be sued by Waymo, that would present serious ethical issues that could lead to Quinn's disqualification."

Quinn Emanuel, in a 27 June filing, said there is no "'Quinn Conflict'", adding that there "are no responsive documents from Quinn Emanuel prior to October 2016, because Waymo did not contact Quinn Emanuel regarding this case until 2017″.