The lawsuit said the agency ordered Twitter to provide the information by 11:45 a.m. on March 13, one day before an official from CBP’s Office of Professional Responsibility actually faxed the summons to the company. With the information requested, Twitter told the court, the CBP would be able to “pierce the anonymity of the person or persons who established and use the @ALT_USCIS account.” Twitter argued that providing the information to the CBP would violate the First Amendment’s free-speech protections.

“Compelled disclosure of the identities of Twitter users who have engaged in pseudonymous speech would chill their exercise of the constitutionally protected right to speak anonymously,” the company said in its original filing. “Moreover, independent of its users’ rights, Twitter’s actions in providing a platform for the dissemination of its users’ speech—including its decision to permit the publication of pseudonymous speech—is fully protected by the First Amendment.”

The operator—or operators—of the @ALT_uscis account, which has more than 33,000 followers, apparently agrees. In a tweet shortly after news of the lawsuit broke, the account posted a screenshot of the First Amendment.

In addition to the constitutional argument, Twitter claimed the CBP order exceeds the legal authority of the federal law under which it was issued. The cited provision, known as Section 1509, allows certain DHS officials to examine a company’s records in “any investigation or inquiry conducted for the purpose of ascertaining the correctness of any entry, for determining the liability of any person for duty, fees and taxes due or duties, fees and taxes which may be due the United States, for determining liability for fines and penalties, or for insuring compliance with the laws of the United States administered by the United States Customs Service.”

But Twitter argued the rationales listed in Section 1509 “clearly relate narrowly to imports,” and said the CBP couldn’t establish that its summons was related to “any investigation or inquiry relating to the import of merchandise.” As it is, it’s highly doubtful the account is involved in the import-export business. In the lawsuit, Twitter said the CBP officer who issued the summons “stated vaguely that he is conducting an investigation,” but offered the company’s legal team no further details about it.

Twitter’s complaint also took a thinly veiled jab at Trump’s recent legal woes. In a larger contention about the legal standards for subpoenas, the company cited Makaeff v. Trump University as precedent. President Trump recently settled that case, a class-action lawsuit accusing his for-profit real-estate seminars of fraudulent business practices, for $25 million.