The National Security Agency reimbursed some of the nation's top tech companies for participating in its PRISM surveillance program, according to new leaked government documents obtained by The Guardian.

The revelation puts a financial spin on what until now has mostly been a question of civil liberties. Previous NSA documents have linked companies such as Google, Facebook, Yahoo and Microsoft to the PRISM program, though many of the companies have denied granting the NSA "direct access" to their servers. Although a Yahoo spokesperson said the government is supposed to reimburse companies for cooperating with federal surveillance requests, the other tech companies either denied receiving money or refused to respond directly to the accusations.

Some critics fear that the shadow revenue flowing to the private sector could create a perverse incentive for tech companies.

"The line you have to watch for . . . is the difference between reimbursement for complying with a lawful order and actually a profit-making enterprise," Michelle Richards, legislative counsel for the American Civil Liberties Union's told The Hill.

Google and Microsoft have asked the government for permission to disclose the aggregate numbers behind the NSA's secret surveillance requests. However, since the companies filed those suits, the Justice Department has asked for (and received) an extension of the deadline six times. It's unclear whether the government can simply continue deferring indefinitely.

Update: In a statement to the Post, Facebook denied receiving payments from the government. "Facebook has never received any compensation in connection with responding to a government data request," a spokesperson said.

Correction: The original version of this post said that Facebook was among the companies that received payment for cooperating with surveillance requests. It was not among them.