But within New York art circles, it was Morgan Art Foundation and the company’s adviser, Simon Salama-Caro, who were better known as the representatives of Mr. Indiana.

The Morgan company says it has served as Mr. Indiana’s agent since the 1990s, when Mr. Salama-Caro sought out the largely forgotten artist who had shut himself away on this island. He struck an agreement with Mr. Indiana under which, in exchange for royalties, the artist authorized Morgan to produce and sell limited editions of some of Mr. Indiana’s most celebrated works, including “LOVE.”

The company and Mr. Salama-Caro were later credited with helping to fuel a comeback for Mr. Indiana, whose profile rose with gallery shows and a major retrospective in 2013 at the Whitney Museum of American Art. Mr. Salama-Caro, who earns commissions on the sales, and his family have also started assembling a full catalog of Mr. Indiana’s work.

The lawsuit contends that the company’s rights have been violated by some of the new work and that the artist’s legacy and market values are threatened by what is described as its inauthenticity and proliferation. The lawsuit named Mr. Indiana as a defendant because he was party to the agreement that Morgan argues has been violated.

Mr. Salama-Caro said that among the troubling recent pieces was “WINE,” a sculpture that mimics the monumental imagery of “LOVE.” The magazine Wine Enthusiast featured the sculpture on its May cover and published an interview with Mr. Indiana, conducted by email, in which he described his long affection for wine and said he had created another work using malbec as a stain.

Barbara Haskell, who curated the Whitney’s Indiana retrospective, said she was surprised that Mr. Indiana had created a “WINE” sculpture. “Whatever four-letter words he used, they were always psychologically charged,” she said. What’s more, Professor Wilmerding and several other friends said they had not known Mr. Indiana to be a wine drinker.