Capitalize a group of related organizations?

I work for the US Department of the Interior. There are more than ten organizations that make up the Department. Bureau of Land Management, Bureau of Ocean Energy Management. Collectively, they are referred to as the bureaus or Bureaus. We would always capitalize each individually, but when referring to the group, some think it should be the bureaus, and others think the Bureaus.

We also have a similar issue with several entities known as the Policy Offices, or policy offices, depending on whom you ask. Will you settle this once and for all? Thanks!