The seal of the Federal Bureau of Investigation is seen at the J. Edgar Hoover building in Washington. (Andrew Harrer/Bloomberg)

A New York man who ran a small Internet company revealed Monday what the government has fought for 11 years to keep sealed: the contents of a national-security letter, a wide-ranging demand for customer data that was issued without a judge’s consent.

The successful plaintiff, Nicholas Merrill, becomes the first person to be allowed by a court to reveal fully what an NSL contained. Merrill was able to do so only after a long battle over his free-speech rights as well as a challenge to the constitutionality of the NSL statute.

“I have spent over a quarter of my life fighting to get my right to speak about this issue back,” said Merrill, 43. “For more than a decade, the FBI has been demanding extremely sensitive information about private citizens from thousands of companies.”

The 2004 NSL, he said, sought cell-tower location data on one of his customers’ phone calls, any “screen names” or online nicknames his customer may have used, any merchandise orders he may have placed, and all e-mail account information, among other things.

Merrill also believes the NSL’s language can be interpreted to include Web searches and Web browsing history. “This kind of content reveals the most intimate details of our lives,” he said in a news conference call.

With such data, he said, the FBI “can unmask anonymous online speakers and expose an individual’s networks of personal contacts and associations, raising important privacy and free speech concerns.”

The FBI has said that it no longer seeks cell-tower data with an NSL but obtains a court order. A Justice Department spokesman in New York had no comment on the case. But in a July filing, an assistant U.S. attorney argued that disclosure of the NSL contents “would reveal exactly” the methods used in FBI national security probes.

“The nondisclosure requirements are lawful,” Assistant U.S. Attorney Benjamin Torrance said, “as the government’s interest in keeping certain matters secret outweighs the interests in public disclosure.” He also said that the FBI might want to shield from disclosure a currently unused but lawful technique because it may be used in the future.

In an interview, Merrill recalled the cold February day in 2004 when an FBI agent from the New York field office showed up at his door, pulled an envelope out of his trench coat and handed it to him.

“I was completely in shock,” said Merrill, whose company, Calyx Internet Access, is now defunct. “When I first looked at the letter, I got stuck at the paragraph where it said I couldn’t tell anyone.”

Nonetheless, he called his attorney, and the case was taken up by the American Civil Liberties Union, with Merrill suing the government as “John Doe.” That year, U.S. District Judge Victor Marrero in Manhattan ruled that the NSL statute was unconstitutional, prompting Congress to amend the law to allow a recipient to challenge the NSL and gag order.

In 2006, the FBI withdrew its data demand to Merrill but maintained the gag order. Two years later, an appeals court held that parts of the amended gag-order provision violated the First Amendment and narrowed the grounds for a gag order. In 2010, Merrill was finally allowed to say he had received the NSL, but he still could not fully discuss its contents.

Last year, his case was taken up by a group of students at Yale University, and in December, Merrill sued again. In August, Marrero ruled that the gag order should be fully lifted.

The judge noted that “many, if not all” of the techniques the FBI sought to keep secret have been disclosed by other government agencies. “Therefore, it strains credulity that future targets of other investigations would change their behavior” if the NSL’s full contents were revealed, Marrero wrote.

The Justice Department did not appeal, and on Monday, the gag order was fully lifted.

Merrill said it should not have taken so long. The burden on NSL recipients to ensure the government’s request is lawful is “completely unreasonable,” he said.

“At this moment, when the public is once again debating whether to expand the scope of the government’s surveillance authorities, we should pause to ensure that we know how existing authorities have been construed in secret,” said Amanda Lynch, a student with Yale’s Media Freedom and Information Access Clinic.

Julie Tate contributed to this report.