Google said on Wednesday that 68 percent of the U.S. government's requests for users' information were without a warrant.
The company said that just 22 percent of the requests used a search warrant, and 10 percent relied on court orders or other processes.
From July to December 2012, Google received 21,389 U.S. government requests for information about 33,634 users. The company said it complied with about 88 percent of those requests.
Data requests have increased 70 percent since 2009, Google said.
The Electronic Communications Privacy Act (ECPA) only requires police to obtain a subpoena, issued without a judge's approval, to read emails, Facebook messages and other electronic communications that have been opened or that are more than 180 days old.
Senate Judiciary Committee Chairman Patrick Leahy (D-Vt.) argues that ECPA, which was passed in 1986, is out of date, and that electronic documents should receive the same level of legal protection as physical documents.
He pushed legislation last year that would have required police to obtain a warrant to read all private Internet communications, regardless of how old they are.
Republicans expressed concern that the warrant requirement could hamper urgent police investigations. Leahy plans to push the measure again this year.
"It is going to be a fight. But I think people are realizing they don't have to give up their ability to use the Internet while at the same time guarding their freedom," Leahy said in a speech at Georgetown University Law Center last week.
—Updated at 4:52 p.m. to note that Google complied with 88 percent of the requests