The letter follows Microsoft's motion in a secret court last month asking for permission to break out which requests were from law enforcement officials and which were from the National Security Agency. It hasn't received a response.
A spokesman for the attorney general said the office is reviewing the letter.
Currently, the company is limited in what it can publicly say about the requests for information and is forced to combine the total requests and report only how many it has received, in increments of 1,000. Microsoft said in June it received between 6,000 and 7,000 requests from both law enforcement and national security officials in the last six months of 2012.
Microsoft's general counsel, Bradford Smith, argues in the letter that the gag order violates the company's constitutional right to free expression, which is constrained only "by a narrowly tailored compelling government interest."
"Numerous documents are now in the public domain. As a result, there is no longer a compelling government interest in stopping those of us with knowledge from sharing more information," Smith wrote.
Technology companies like Google, Facebook and Microsoft have come under fire for cooperating with the NSA's Prism program, in which the government seizes records including emails, chats and video calls. The system was exposed by The Guardian and Washington Post newspapers in a series of stories that began in June and which relied on documents supplied by former NSA contractor Edward Snowden.
Smith also clarified in a blog post Tuesday the company's position mainly in response to a story in The Guardian last week that said Microsoft gave the U.S. government special access to unencrypted emails and video calls over its Skype service.
He reiterated that Microsoft did not give the government unfettered access to its servers, but turned over information regarding specific accounts after reviewing the legality of the requests.
Smith said Microsoft did not give the government the ability to break into encrypted emails. Rather, he said the company turned over material from its servers, where data remains unencrypted.
He also said that back-end improvements to Skype "were not made to facilitate greater government access to audio, video, messaging or other customer data." Smith also said that Microsoft has never turned over data about business or government clients to any government based on a national security request.