We've believed the answer is probably "no". But in the LA Times last summer the lawyers for a presbyterian minister who is under trial (in church courts) for performing a same-sex wedding against church law, is arguing the law can pressure clergy who refuse to perform same-sex weddings:

Spahr's trial, which will be held in Napa, begins less than three weeks after a federal court judge ruled that California's ban on same-sex marriage is unconstitutional. And it underscores the awkward position in which changing civil law places many clergy members.

Although the Presbyterian constitution does not explicitly prohibit same-sex marriage, it defines marriage as "a civil contract between a woman and a man." But same-sex marriage is legal in five states and the District of Columbia and is working its way through the courts in California.

"More and more ministers are going to be put in a position where their church members are going to come to them asking for a wedding, and they're going to have to say yes," said the Rev. Beverly Brewster, Spahr's defense attorney. "Not to do so would violate many constitutional provisions about non-discrimination in pastoral care."