In 1971, the Supreme Court ruling in New York Times Co. v. United States held
that the newspaper was allowed to publish classified government documents.
They said that this was protected under ?

They said that this was protected under the First Amendment.

Explanation:

In 1971, the New York Times was trying to publish classified Pentagon papers but the government under President Richard Nixon was trying to force the newspaper to cancel that publication. The Supreme Court ruled on this matter  and said that the First Amendment that refers to the freedom of speech or of the press protected the right of the New York Times to publish the documents. According to this, the answer is that they said that this was protected under the First Amendment.