The newspaper reported that the company gave technical assistance to the NSA in carrying out a secret court order allowing wiretapping of all Internet communications at the headquarters of the United Nations, an AT&T customer.
The company helped the spy agency in a broad range of classified activities, the newspaper reported.
The documents describe how the NSA's working relationship with AT&T has been particularly important, enabling the agency to conduct surveillance, under various legal rules, of international and foreign-to-foreign Internet communications that passed through network hubs in the United States.
AT&T installed surveillance equipment in at least 17 of its U.S. Internet hubs, far more than competitor Verizon Communications Inc, the Times reported. AT&T engineers also were the first to use new surveillance technologies invented by the NSA, the Times reported.
"This is a partnership, not a contractual relationship," according to one NSA document describing the link between the agency and the company.
AT&T's "corporate relationships provide unique accesses to other telecoms and I.S.P.s," or Internet service providers, according to another NSA document.
AT&T started in 2011 to provide the NSA more than 1.1 billion domestic cellphone calling records daily after "a push to get this flow operational prior to the 10th anniversary of 9/11," referring to the Sept. 11, 2001, attacks on the United States, the Times reported.
AT&T's providing of foreign-to-foreign Internet traffic has been especially important to the NSA because large amounts of the world's Internet communications pass across U.S. cables, the Times reported. The company gave access to contents of transiting email traffic years before Verizon started in March 2013, the Times reported.
Asked to comment on the Times report, AT&T spokesman Brad Burns told Reuters by email: "We do not voluntarily provide information to any investigating authorities other than if a person's life is in danger and time is of the essence. For example, in a kidnapping situation we could provide help tracking down called numbers to assist law enforcement."
Burns said AT&T would have nothing further to say on the report.
© Thomson Reuters 2015