For an organization, whether it be a church or a non for profit, to qualify for tax exempt status one of the requirements is that they not attempt to influence legislation as a substantial part of its activities and it may not participate at all in campaign activity for or against political candidates.
But how often do we hear about megachurches singing the praises of Bush? The requirement is rarely followed, and seldom enforced since the politicians owe their very position to the churches.
That's why it's especially refreshing to see megachurch pastor preaching to uphold this. Rev. Gregory A. Boyd of the Woodland Hills Church was irritated by the repeated requests to endorse conservative political figures and causes. In response he gave a six part sermon series in which he said the church should "steer clear of politics, give up moralizing on sexual issues, stop claiming the United States as a “Christian nation” and stop glorifying American military campaigns." He insists that many Christians have lost their focus on God and instead began worshipping the false idols of the Republican party and its platform in a sort of "idolatry".
But this is not what members wanted to hear. The church lost roughly 1/5 of its members in response. Some members left saying "You’re not doing what the church is supposed to be doing, which is supporting the Republican way."
I'd recommend reading the whole article as there's many more gems in there.