The IRS threat is an empty threat. Pastors can just tell the flock to use the ten percent they were giving for their own charity. No money, no tax.
Actually the larger problem as I see it is if the church loses tax-exempt status on their operations, they would also lose tax exempt status on their properties. How many churches will bow a knee when the alternative is paying taxes on their properties at commercial property rates? I would guess a lot. This is mostly why I do not support the concept of a corporate church. We would be better off meeting in house churches, IMHO.