Who Pays for Shared Sewage Line Backups?

This question was submitted by Samuel P out of Alabama

In my building, we have four apartments, two upstairs and two downstairs, all attached to one sewer line. The sewer backed up inside apt A. Plumber was called, and it's fixed now, but the board told me I have to pay the bill. Apartment A and B have been empty for a while.

What actions can I take?