Reports that have come to light of a secret program of Yahoo to search the incoming emails of customers have provoked other tech giants to deny receiving requests of a similar nature from the U.S. government.

The program was created in 2015 through an order from the government that was classified and involves Yahoo searching hundreds of millions of its user accounts at the request of the FBI or the National Security Agency.

Other tech companies in the U.S., including Microsoft, Google, Facebook and Twitter have denied doing something similar. Most said as well that they would challenge that type of request through court action.

Advocates for privacy said the enlisting of Yahoo by the government to assist in monitoring email was wrong.

An ACLU attorney said it appears that the order Yahoo was issued appeared to be both unconstitutional and unprecedented.

Other opinions exist amongst legal experts. The issue said one legal expert underscores the gray area of legal issues that today’s tech industry and the government of the U.S. have not yet clarified.

It is common knowledge that on a routine basis the U.S. government requests data of users from the U.S. tech industry to help in its surveillance.

Former contractor with the NSA Edward Snowden was instrumental in exposing additional details of the practices the government carries out.

The initiative with Yahoo might have gone further than other requests for information by being broader in scope.

It was reported, that Yahoo was searching through incoming emails of every customer in real time, which means it might have been spying on users that were outside the United States.

It is also possible that the spying violated other countries’ privacy laws, said a legal expert. Europe for example, said the expert, has much stricter privacy rights than does the U.S.

Experts in cybersecurity also question whether the tech giant had complied with other requests from different foreign governments.

Yahoo to date has not publicly given out any details of this program or even given confirmation that it exists. Tuesday afternoon the company released a statement that said it was a law-abiding company that complies with U.S. laws.

The mass searching program for Yahoo emails could be one of many already setup, said the chief of a security firm that specializes in Internet security. Internet companies said the security expert are increasingly encrypting data, which makes to harder for authorities to extract any information via their own surveillance methods.