A few weeks ago Eric Bearse, the spokesperson for Rick Perry's "The Response" prayer rally, explained that people of all faiths were welcome to participate in the event and "seek out the living Christ."
Organizers have made it abundantly clear that this is an exclusively "Christian prayer meeting" ... and according to this email from Allan Parker of The Justice Foundation, who was part of an organizing conference call for the event, it has to be that way because the inclusion of other faiths "would be idolatry of the worst sort":
Recently, I was very privileged and honored to be on a conference call with national religious leaders and Governor Rick Perry. He explained his call for a national solemn assembly to repent and seek the Lord on August 6 in Houston, Texas. I believe the Lord is calling Rick Perry to lead us in a day of national repentance before the Lord. It is a solemn assembly according to Joel 2. As we are approaching the end times, it is even more important than ever for the Body of Christ to pray and seek His face. We must repent and turn from our wicked ways so that God may heal our land.
This is an explicitly Christian event because we are going to be praying to the one true God through His son, Jesus Christ. It would be idolatry of the worst sort for Christians to gather and invite false gods like Allah and Buddha and their false prophets to be with us at that time. Because we have religious liberty in this country, they are free to have events and pray to Buddha and Allah on their own. But this is time of prayer to the One True God through His son, Jesus Christ, who is The Way, The Truth, and The Life.
Parker's email also contained a link to a message [PDF] from Gordon Klingenschmitt who warns that the event "may be interrupted by Muslims who are already demanding to share our stage to pray to Allah."