King & Spalding's prior legal work for WhatsApp Inc. should not disqualify the firm from representing an adversary that was sued by the popular text messaging service in California federal court, lawyers for the firm told a judge Friday.

WhatsApp, represented by Cooley LLP, sued King & Spalding client NSO Group Technologies last year over claims the Israeli cybertechnology company exploited the messaging platform in an effort to gain unauthorized access to user communication. NSO has denied the allegations.

WhatsApp's lawyers contend King & Spalding's work for the company in a sealed matter four years ago has given the firm an unfair advantage in the pending case in Oakland's federal trial court. The Cooley lawyers argued in their disqualification papers that the lawsuit against NSO is substantially related to the earlier sealed matter and that King & Spalding acquired confidential information material to the pending litigation.

On Friday, King & Spalding's lawyers at Long & Levit disputed that the two cases are related, and they argued that three of the four King & Spalding lawyers who worked on the earlier sealed matter are no longer at the law firm. One of those attorneys, Christopher Wray, a former white-collar partner, was confirmed in 2017 as the FBI director.

"Disqualification is a drastic, disfavored and disruptive remedy that is unwarranted here," San Francisco lawyer Jessica MacGregor of Long & Levit said in the new court filing. MacGregor argued that "depriving NSO of highly skilled counsel of its choice will impose significant hardship and prejudice."

New filings in the case in April led to widespread public attention that contrasted Wray's advocacy for WhatsApp as a private lawyer and his statements as FBI director questioning technological barriers that can impede law enforcement investigations.

Indeed, FBI and Justice Department leaders have long clashed with Silicon Valley over encryption.

"Like all other lawyers, [Wray's] duty of loyalty was to his client, and he did not put his personal views ahead of his clients' interests or allow them to affect the legal work he did for clients," the FBI said in a statement in April, according to The Wall Street Journal. "Today, as director of the FBI, his duty is to act in the best interests of the American people."

Wray had been a partner at King & Spalding for 12 years before he left the firm to join the Trump administration in 2017. He reported earning more than $14 million from the firm in the years leading up to his departure, according to financial disclosure filings that are mandatory for many senior-level executive branch employees. His clients included Credit Suisse Group, Johnson & Johnson, Wells Fargo and Chevron, the disclosures showed. He declined to identify three confidential clients who at the time were subject to nonpublic investigations.

Cooley Cooley offices in Washington, D.C. (Photo: Diego M. Radzinschi/ALM)

Cooley lawyers representing WhatsApp assert that King & Spalding acquired information about confidential aspects of the messaging service's platforms when the firm provided legal advice to the company in 2015 and 2016.

The current case "involves the very technology that WhatsApp previously hired King & Spalding to analyze and protect," the Cooley lawyers said.

"King & Spalding is violating a bedrock requirement of attorney loyalty: the duty to avoid switching sides and opposing a client that it once represented," Cooley partner Michael Rhodes said in a filing in April.

Rhodes said in the filing: "Put simply, no client would ever expect to reveal the proprietary and nonpublic details of its product to its lawyers, only to find those lawyers acting adversely to it a few years later on a case involving the same technology and on behalf of a client that marketed and sold the ability to attack and exploit its network."

King & Spalding billed WhatsApp about 94 hours of work on the sealed matter, Long & Levit's MacGregor said in Friday's filing. Wray worked for WhatsApp with King & Spalding lawyers Paul Mezzina, Nick Oldham and Cathy O'Neil, who has since died. Oldham left the firm in 2017 and now serves as the chief privacy and data governance officer at Equifax. Mezzina rejoined the firm earlier this year after clerking for Justice Neil Gorsuch on the U.S. Supreme Court.

NSO retained King & Spalding after a three-month search for a firm to defend the company against WhatsApp's claims. The company said it sought a firm with a bench in cybersecurity, government relations and national security, according to court records. Many firms, MacGregor said, faced conflicts based on work for Facebook, which owns WhatsApp.

"Forcing a change in counsel will send NSO back into a diminished legal marketplace dominated by Facebook," MacGregor wrote. "NSO will also lose the benefit of the significant work K&S has already performed and would have to shoulder the increased expense of beginning anew with replacement counsel."