The Electronic Privacy Information Center (EPIC) even sued in an unsuccessful attempt to force the Federal Trade Commission to block Google from changing its policies.
The New York Times drew attention to Microsoft's privacy changes with a story Friday.
Microsoft has said that unlike Google, it will not use the personal information for targeted advertising, but the revised policy does not forbid that.
Markey asked Microsoft to explain why the new policy does not prohibit targeted advertising.
Christina Pearson, a Microsoft spokeswoman, said the company will revise its policy.
"One thing we don’t do is use the content of our customers’ private communications and documents to target advertising. However, we recognize we could have been clearer about this when we rolled out our updated services agreement," she said in a statement. "We appreciate the feedback we’ve received, and as a result, we will update the agreement as soon as possible to make that point absolutely clear."
"Over the years we have consistently informed users that we may use their content to improve the services they receive," she said. "For instance, we analyze content to improve our spam and malware filters in order to keep customers safe. We also do it to develop new product features such as email categorization to organize similar items like shipping receipts in a common folder, or to automatically add calendar invitations."
Markey asked Microsoft to explain what customer information it shared across its services before the changes and what it is able to now share after the changes. He also requested a list of all the services affected by the revision.
He asked whether users will have any way to opt out of the changes and how Microsoft will handle the information of children and teens.
—Updated with an expanded statement from Microsoft at 5:28 p.m.