Following Google's lead, Microsoft revealed data on Thursday about the number of police requests for user data it received for services including Hotmail, Outlook, Xbox Live and Skype.
The company said that last year, it received 75,378 police requests for customer information from around the world, covering 137,424 accounts. Microsoft said it disclosed customer content, such as the texts of emails, in response to only 2.1 percent of those requests, or 1,558 times.
More than 99 percent of the time it disclosed content was in response to a warrant from a U.S. court, Microsoft said.
Google was the first Web company to disclose detailed information about its compliance with police requests for user information. The company said that it received 42,427 police requests last year and that it provided at least some data about two-thirds of the time. Twitter has also begun periodically disclosing data on police requests.
Google and Twitter also revealed information about requests to take down material.
"We’ve benefited from the opportunity to learn from them and their experience, and we seek to build further on the industry’s commitment to transparency by releasing our own data today," Microsoft General Counsel Brad Smith wrote in a blog post.
House and Senate lawmakers are working on legislation to expand the privacy protections for email and other private online content.
Under current law, police only need a subpoena, issued without a judge's approval, to read emails that have been opened or that are more than 180 days old. Privacy advocates argue the law is woefully out of date and that police should need a warrant to access sensitive online messages.
Microsoft, Google, Yahoo and Facebook all say they already require a warrant for private online content. They argue that the Fourth Amendment provides their customers with greater privacy protection than current federal law.