The Marxist Internet Archive, a website devoted to radical writers and thinkers, recently received an email: It must take down hundreds of works by Karl Marx and Friedrich Engels or face legal consequences.

The warning didn’t come from a multinational media conglomerate but from a small, leftist publisher, Lawrence & Wishart, which asserted copyright ownership over the 50-volume, English-language edition of Marx’s and Engels’s writings.

To some, it was “uncomradely” that fellow radicals would deploy the capitalist tool of intellectual property law to keep Marx’s and Engels’s writings off the Internet. And it wasn’t lost on the archive’s supporters that the deadline for complying with the order came on the eve of May 1, International Workers’ Day.

“Marx and Engels belong to the working class of the world spiritually, they are that important,” said David Walters, one of the organizers of the Marxist archive. “I would think Marx would want the most prolific and free distribution of his ideas possible — he wasn’t in it for the money.”

Still, Mr. Walters said the archive respected the publisher’s copyright, which covers the translated works, not the German originals from the 19th century. On Wednesday, the archive removed the disputed writings with a note blaming the publisher and a bold headline: “File No Longer Available!”

The fight over online control of Marx’s works comes at a historical moment when his ideas have found a new relevance, whether because the financial crisis of 2008 shook people’s confidence in global capitalism or, with the passage of time, the Marx name has become less shackled to the legacy of the Soviet Union. The unlikely best seller by the French economist Thomas Piketty, “Capital in the 21st Century,” harks back to Marx’s work, examining historical trends toward inequality in wealth.

Despite this boomlet in interest, however, Lawrence & Wishart, located in East London, hardly expects to have an online hit on its hands, said Sally Davison, the publisher’s managing editor. The goal is to create a digital edition to sell to libraries in place of a print edition, which costs roughly $1,500 for the 50 volumes.

“Creating a digital strategy is key to our survival,” she said. “We are currently negotiating with somebody, that’s why we’ve asked the archive to take it off; it’s hard to sell it to librarians if a version already exists online.”

Lawrence & Wishart has been losing the argument online, however. The publisher said that it had received about 500 irate emails, along the lines of “How can you say you are radicals?” There are more than 4,500 signatures on an online petition to oppose the notion of a copyright claim on Marx’s and Engels’s writings; the petition cites the incongruity, noting that the two philosophers “wrote against the monopoly of capitalism and its origin, private property, all their lives.” And the libertarian Cato Institute enjoyed teasing its ideological adversaries with an I-told-you-so blog post titled, “Because Property Rights Are Important.”

Ms. Davison said she was flabbergasted to see Lawrence & Wishart cast as the oppressor. The publisher has two full-time employees and two part-time employees and barely makes ends meet, publishing a handful of journals, like Anarchy Studies, and about a dozen left-wing books a year, she said.

“We make no profit and are not particularly well paid,” she said.

Ms. Davison defended her position by quoting Marx to the effect that you must adapt to real-world conditions: “We don’t live in a world of everybody sharing everything. As Marx said, and I may be paraphrasing, ‘We make our own history, but not in the conditions of our own choosing.’ ”

The publisher also tried to turn the tables on its critics, questioning whether it was indeed radical to believe that there is no ownership of content produced through hard work, like the mammoth translation and annotation of Marx’s and Engels’s work, a project initially directed by the Soviet Union in the late 1960s that took some 30 years of collaboration among scholars across the world.

In a note on its site, Lawrence & Wishart said its critics were not carrying on the socialist and communist traditions, but reflecting a “consumer culture which expects cultural content to be delivered free to consumers, leaving cultural workers such as publishers, editors and writers unpaid, while the large publishing and other media conglomerates and aggregators continue to enrich themselves through advertising and data-mining revenues.”

The statement noted that many works by Marx and Engels — including “The Communist Manifesto,” which urges, “Workers of the world, unite!” — were freely available in translation on the nonprofit archive and other sites.

Ms. Davison said, “This is a 50-volume, academic edition; it isn’t necessary to revolutionary activity,” and noted that much of the material included things like “Marx writing to Engels asking if you want to come by my house to go to this meeting.”

Because of how the complete works of Marx and Engels were translated into English, Ms. Davison said, the copyright had been shared among three publishers: Progress, a company in the Soviet Union that no longer exists; Lawrence & Wishart, once the official publisher of the British Communist Party; and the radical New York publishing house, International Publishers. Lawrence & Wishart, she said, has taken the lead in trying to form a digital strategy.

She said she expected a deal to take effect by early next year, and Lawrence & Wishart and International Publishers both said they would discuss how to divide the proceeds.

Even without the removed Marx and Engels material — consisting mainly of early philosophical and economic writings, as well as notes and letters in which their ideas were first hashed out — the Marxist Internet Archive still will host roughly 200,000 documents in more than 40 languages from political theorists and economists.

Peter Linebaugh, a professor at the University of Toledo in Ohio, who has studied the history of communism, said that the comprehensive English translation of Marx’s and Engels’s writings was a galvanizing event, and that he had great respect for the effort that went into pulling it off. He expressed disappointment over the publisher’s move, and disputed the idea that you could divide Marx’s work into the important and the mundane. “What seems like arcane scholarship,” he said, “can appear as a bombshell to young militants.”

Surveying the entire affair, he concluded, “This is the triumph of capitalism, having the small fish biting at each other.”