Rubin Law Firm PC filed suit in the Northern District of California Thursday, seeking to represent a class of Westlaw subscribers allegedly overpaying for baseline subscriptions due to the loss of competition from Casetext.
The suit alleges that Thomson Reuters' acquisition of Casetext violated the Clayton Act and includes claims of restraint of trade, monopolization and violation of the Cartwright Act, California's antitrust law.
"This case targets a classic technology sector 'killer acquisition' executed by an entrenched duopolist with market power to suppress a disruptive upstart, eliminate downstream pricing discipline, and lock legal professionals into artificially inflated, supra-competitive pricing tiers," the complaint said.
Casetext entered the legal research market in 2013 to offer a "budget-conscious" alternative to Thomson Reuters and LexisNexis' services, which the complaint says have long dominated the U.S.'s premium digital legal research market. The complaint says Casetext served as a "vital competitive anchor" in the industry and provided a check on the ability of the larger incumbents to raise prices.
In 2023, Casetext launched "the world's first" generative artificial intelligence legal assistant, called CoCounsel, according to the complaint, and the company's "market disruption accelerated exponentially."
"Enterprise law firms rushed to purchase Casetext subscriptions on top of or in lieu of their existing platforms," the complaint said. "Casetext's rate of market share growth and adoption velocity dramatically outpaced the stagnant, single-digit growth rates of Westlaw and LexisNexis."
Rather than spend the time and capital needed to build a comparable large language model, the complaint alleges Thomson Reuters decided to "short-circuit the competitive process" by agreeing to buy Casetext for $650 million in cash. Having neutralized the competitive threat, the complaint alleges that Thomson Reuters shuttered the standalone Casetext platform in 2025.
Casetext users were then forced to use Westlaw, where baseline subscriptions are considerably more expensive, the suit says.
"Simultaneously, existing Westlaw subscribers were completely stripped of the competitive 'Casetext alternative' leverage they historically weaponized to negotiate or suppress their Westlaw annual renewal escalators," the complaint said.
According to the suit, Rubin Law Firm paid around $32.50 per month for the Casetext service and was forced to migrate to Westlaw last year, paying $111.48 per month, with built-in annual increases.
The proposed nationwide class would cover baseline Westlaw subscribers, meaning those who do not also subscribe to Westlaw's separate AI-based legal platform, currently known as CoCounsel.
A representative for Thomson Reuters told Law360 in a statement Friday that the company has not been served with a complaint related to the matter.
"Until we have received and reviewed any such filing, we are not in a position to comment," the statement said.
Representatives for the proposed class did not immediately respond to a request for comment Friday.
The proposed class is represented by Roy A. Katriel of the Katriel Law Firm PC and Ralph B. Kalfayan of the Kalfayan Firm APC.
Counsel information for Thomson Reuters was not immediately available.
The case is Rubin Law Firm PC v. West Publishing Corp. et al., case number 3:26-cv-11239, in the U.S. District Court for the Northern District of California.
--Editing by Drashti Mehta.
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