I can see this as discrimination if they are unwilling to honor bulletins from churches such as UU, FSM, Humanism (not to mention temples, mosques, etc.)... that would be a clear violation of discrimination.

Personally, I think this is the best way to handle something like this...
There was, not too long ago, someone who presented a UU bulletin in response to a Denny's in TX which likewise offered the 10% discount. The discount was honored, but the following week the offer was no longer being advertised.

Should the business refuses to honor the bulletin from non-xtian churches, they will rightfully have a lawsuit on their hands.

Over at Think Progress they mention:
When Newsweek ran a picture of Palin in a running outfit on its cover this month, Palin and many others criticized the magazine for being sexist. Beck joined the outrage, saying the “attack” on Palin was “dizzying” and “devastating.” He said Newsweek had reached “the highest of the lows” and added that the magazine now “sucks.”
http://thinkprogress.org/2009/11/26/beck-palin-ki...

Yet it's ok for Beck to make degrading remarks about Palin. *eye roll*