Mr. Saulignac said, “There is no clear frontier in the law between journalists who follow the rules, and all the rest.” Mainstream journalists, he said, “could be attacked for fake news, simply because, for instance, you have attacked me.”

Beyond that, he said, “How can it be proved in just 48 hours that I don’t have an account in the Bahamas?”

“At a time when the press is threatened around the world, it is better to protect the press,” Mr. Saulignac said.

Mr. Macron’s ambiguous attitude toward journalists has been much commented on in the French news media. Tellingly, he announced his fake news measure, in a tone of admonition, to mainstream journalists who had gathered in January for the traditional presidential New Year’s greeting to the press.

If any group of journalists in France needed no warning about steering clear of unverified information, it was that one. Yet Mr. Macron made a point of telling those gathered that they needed principles and an ethics code, before announcing the new bill.

Journalists, an exasperated Mr. Macron told a television interviewer last fall during a school visit, “are too interested in themselves, and not enough in the country.” Journalists, he said, “don’t interest me, it’s the French who interest me. That’s what you’ve got to understand.”

Patrick Eveno, a professor of media history at the Sorbonne, said he saw good and bad in the legislation. He said it “puts the problem of false information in the public square, and that’s important.” Yet it may be ineffective, he said, because “it’s extremely difficult for a judge in 48 hours, in an electoral period, to decide what is fake news.”