Senate Rules opined on official Facebook pages for Senators, according to this Roll Call report.  I’ll post any documentation on the move when I find it.  Here’s an earlier story on what was being considered.

A growing number of senators have Facebook pages and some have received attention for their Twitter use. But confusion continues over how exactly franking rules affect use of Facebook and other social networking sites.

Senators face relatively few rules for how their campaigns use third-party sites, but official use remains “a gray area,” one staffer said.