Senators this week face one of the trickiest series of votes they’ll confront this year: on how to reform the U.S. Postal Service.

On Tuesday, the Senate is set to vote on up to 38 amendments to a major bipartisan bill that would reform the Postal Service, including proposals to end six-day mail delivery, continue six-day mail delivery, require USPS to wait two more years before closing small rural post offices, and to close post offices on Capitol Hill.