A New York man who ran a small Internet company has sued the Justice Department to lift a 10-year-old gag order that accompanied a national security order served on him by the FBI for a customer’s records.

In a lawsuit filed Thursday, Nicholas Merrill charged that the U.S. government has violated his First Amendment rights by imposing what he says amounts to a permanent gag order forbidding him from speaking about a national security letter he received in 2004 — even though the underlying investigation has apparently ended.

National security letters (NSLs) are a form of administrative subpoena issued by the FBI in national security investigations without court approval. In particular, Merrill wants to be able to talk about the specific types of records the government demanded that he disclose, which he refused to do.

The NSL non-disclosure provision bars him from doing that.

“It’s really long past due that we have an open and public discussion about how warrantless searches are being used against Americans,” Merrill, 42, said in an interview. “To the extent that the government keeps everyone who receives these letters under lifelong gag orders, the very people who know how they are used are prevented from talking about them.”

The public has little idea how broadly the FBI has interpreted its authority to use NSLs, Merrill’s attorneys wrote in a complaint filed in U.S. District Court for the Southern District of New York.

Merrill wants the court to declare both the NSL statute and its non-disclosure provision unconstitutional under the First Amendment. He also wants the gag order — parts of which had been lifted four years ago — to be entirely removed.

It is the latest legal action in his decade-long battle with the government over the issue.

FBI and Justice Department officials said they cannot comment on pending litigation, but the government has argued in his earlier cases that disclosing the types of records sought can reveal investigative techniques that might threaten open cases.

Merrill, whose now-defunct company, Calyx Internet Access, offered e-mail accounts and space on the Internet where clients could maintain their own Web sites, first sued the government in 2004 after he was served with the NSL. He challenged the constitutionality of the substantive authority and the secrecy requirement, which barred him from even revealing he had received an NSL.

He was the first NSL recipient ever to challenge such an order in court.

In 2004, a federal court in the Southern District of New York ruled the statute violated the First Amendment. Two years later, the FBI withdrew the demand for the records but maintained the gag order.

In 2007, Merrill wrote an anonymous opinion piece published in The Washington Post describing how “stressful and surreal” it had been to live under such enforced silence.

An appeals court in 2008 held the gag order was unconstitutional but said the violation could be remedied if the FBI could show “good reason to believe that disclosure may result in” harm to an international terrorism or clandestine intelligence investigation.

The government eventually settled with Merrill in 2010, allowing him to identify himself. Though he came forward to disclose his experience, he was still barred from identifying all the categories of data demanded.

In February, Merrill sought help from the Media Freedom and Information Access Clinic at Yale Law School, which got the FBI to modify the gag order again, this time permitting Merrill to reveal the identity of the target and the fact that he did not turn over any records. But officials insisted that he keep quiet on the types of data sought, citing harm to investigations, said Lulu Pantin, a student at the access clinic.

Earlier this year, Merrill told his client about the NSL. The person, he said, “was somewhat surprised, but also not surprised. This person has undergone a lot of government harassment over a long period of time . . . and they are very cynical about the fairness of the legal system.”

Merrill said that he would have done the same thing for any client “because for me the principle was the violation of the Constitution and the obvious illegality of the request.”

The gag is particularly burdensome, Merrill contends, because he speaks publicly on surveillance and digital privacy and directs a nonprofit organization, the Calyx Institute, which promotes secure online communications.

The complaint also states that the FBI’s actions since 2010 reveal that the investigation that prompted the NSL has concluded.

Merrill’s attorneys noted that the long-running gag order runs contrary to President Obama’s direction to the attorney general, stated in a major surveillance speech in January, to amend the use of NSLs so that “this secrecy will not be indefinite” and that the gag order will terminate within a fixed time.

Merrill and several other recipients of NSLs have filed a joint friend-of-the-court brief in another case involving two unnamed companies that have sued the U.S. government over the constitutionality of the NSL statute. That case, being argued by the Electronic Frontier Foundation, is pending before the U.S. Court of Appeals for the 9th Circuit in California.