"Safeguarding Americans’ privacy rights is not a Democratic issue or a Republican issue— it is something that is important to all Americans, regardless of political party or ideology," Leahy said in a statement on Monday.
The Senate Judiciary Committee approved similar legislation last year, but the proposal never made it to the floor for a vote.
Reps. Zoe Lofgren (D-Calif.), Ted Poe (R-Texas) and Suzan DelBene (D-Wash.) have introduced legislation in the House that would require a warrant to access mobile location data in addition to emails and other online messages.
At a House hearing last month, a Justice Department official agreed that there is "no principled basis" for treating emails differently depending on how old they are.
Traditionally, the courts have ruled that the Fourth Amendment provides only limited privacy rights for information that people share with third parties. Some law enforcement groups have argued that this means they only need a subpoena to compel email providers, Internet service companies and others to turn over their customers' sensitive content.
An appeals court ruled in 2010 that police violated a man's constitutional rights by searching his emails without a warrant, but the Supreme Court has yet to settle the issue.