Twitter is suing the US government to prevent the Trump administration from forcing it to reveal who's running an anti-Trump account.

In a lawsuit filed Thursday, Twitter says an arm of the Department of Homeland Security used a "limited-purpose investigatory tool" in an effort to unmask the identity of the person or people behind @ALT_uscis, an account that criticizes the administration's management of US Citizenship and Immigration Services. USCIS is part of DHS.

According to the suit (PDF), US Customs and Border Protection, another part of DHS, issued a summons on March 14 demanding that Twitter release records that would lead to the account's owners. The company says the order is unlawful and must be dismissed.

"Permitting CBP to pierce the pseudonym of the @ALT_uscis account would have a grave chilling effect on the speech of that account in particular and on the many other 'alternative agency' accounts that have been created to voice dissent to government policies," Twitter wrote in its suit.

The company declined to comment beyond the lawsuit for this story. DHS declined to comment. The White House didn't immediately respond to a request for comment.

The account, which identifies itself as "immigration resistance" and states it doesn't represent DHS or USCIS, is one of dozens of "alternative" government agency accounts that sprung up after Donald Trump was inaugurated as the country's 45th president. Other alt-accounts include @AltUSNatParkService, which bills itself as "The #Resistance team against #AltFacts#FauxNews #FauxScience," and @RogueNASA, "The unofficial "Resistance" team of NASA."

The person or persons behind the @ALT_uscis didn't immediately respond to a direct message seeking comment. But the account pinned a tweet of the First Amendment, which protects free speech, to the top of its page.

It also tweeted:

In its lawsuit, Twitter argued the people behind anti-Trump accounts, some of whom say they're government employees, risk harassment and retaliation, as well as their jobs, if their real identities are revealed.

In the suit, Twitter says the summons and the laws behind it don't apply to the social network's users. They are typically issued in cases in which the Customs Service finds something suspicious with merchandise being imported.

"CBP's investigation of the @ALT_USCIS account plainly has nothing whatsoever to do with the importation of merchandise in the United States," Twitter said in its suit.

The social network accused the US government of violating the First Amendment in an attempt to silence political speech. The @ALT_uscis account was created around the time Trump issued an immigration curb in January, which was later blocked by courts.

Roy Gutterman, a media law expert at Syracuse University, said the Trump administration's move seems to be an effort to root out critics and appears to violate the First Amendment.

"America has a long history of protecting critics of government and Twitter is a modern form of expression and criticism," Gutterman said. "In this case, it's even more nefarious because the government is trying to find out who's saying bad things about it because that person or people could very well be working for the government."

On March 14, CBP agent Adam Hoffman sent a fax to Twitter, demanding the website provide the agency with user names, login information, phone numbers, mailing addresses and IP addresses behind the account. The summons threatened further court action if Twitter didn't comply.

The agency also set a deadline of March 13, one day before the summons was actually faxed. The agency also asked that Twitter keep the summons under wraps for "an indefinite period of time."

You can see the summons here:

Twitter notified the @ALT_uscis account owners on April 4, according to the lawsuit.

The American Civil Liberties Union plans to join Twitter and said it will be filing documents in court on the account's behalf.

"To unmask an anonymous speaker online, the government must have a strong justification," ACLU attorney Nathan Freed Wessler said in a statement. "But in this case, the government has given no reason at all, leading to concerns that it is simply trying to stifle dissent."

Twitter has unmasked accounts in the past, like when it helped the FBI catch the Twitter user who sent an seizure-inducing GIF as part of a hate crime.

First published, 1:09 p.m. PT.
Updated, 2:01 p.m. PT: To include remarks from the ACLU, and more details from Twitter's lawsuit.

Updated, 3:59 p.m. PT: To include expert opinion, more detail.

Life, disrupted: In Europe, millions of refugees are still searching for a safe place to settle. Tech should be part of the solution. But is it? CNET investigates.

Tech Enabled: CNET chronicles tech's role in providing new kinds of accessibility.