Greenberg Traurig has been hit with a $100m malpractice suit over allegations that it failed to properly prosecute patents for a longstanding electronics manufacturing client and committed discovery abuses in related litigation.

Leviton Manufacturing sued Greenberg and three of its former intellectual property (IP) partners after the company itself was sanctioned earlier this year for the conduct of Greenberg lawyers in prosecuting Leviton patents.

Leviton claims the Greenberg lawyers were "disloyal to their long-time client" and "put their own interest in earning fees in a case where they were barred from appearing as counsel" ahead of their client's interests.

The Leviton suit stems from a May ruling that Leviton's counsel at Greenberg had committed discovery abuses and deceived the US Patent and Trademark Office in filing patent applications. Leviton is appealing that ruling in which the judge fined the company more than $1.04m (£643m).

The Leviton suit names as defendants the firm and three of its former lawyers – Paul Sutton, Barry Magidoff and Claude Narcisse.

In separate statements, both Greenberg and Sutton called the claims "without merit" and said they would vigorously defend themselves. Greenberg said some of the claims "contradict arguments that Leviton has made in another court."

Sutton, who now practises with Magidoff at Sutton Magidoff, began representing Leviton in 1971 on its IP matters.

Leviton matters formed half or more of Sutton's book of business and the company followed him as a client whenever he changed firms, the suit claims.

Greenberg Traurig brought Sutton in as a partner in February 2000 from Thelen Reid & Priest. According to the complaint, Leviton on average paid Greenberg $4.9m (£3m) a year in fees. Between 2000 and 2005, it claims it paid Greenberg more than $38m (£23.5m).

Since 1998, Sutton has helped Leviton file patent applications for technological improvements to devices called ground fault circuit interrupters. Those devices are common in most homes and buildings and are designed to protect people from electric shock by interrupting a circuit when a broken path to the ground occurs.

Leviton claims Sutton did not prosecute patent claims "that covered the full breadth" of the technology.

Leviton claims it had to pay millions of dollars in "excessive fees for a multiplicity of patent application filings in excess of what a patent prosecutor of ordinary skill" would have achieved in following accepted practices. It also claims it was harmed by "widespread infringement" of an improvement known as isolated conductors because it did not until recently have proper patent coverage.

This article first appeared in the New York Law Journal, a US sister title of Legal Week.