One of America’s biggest groups of Christian colleges is fragmenting over the issue of gay marriage.

Union University, a Southern Baptist school in Tennessee, announced Wednesday that it is leaving the Council of Christian Colleges and Universities (CCCU). The reason? Two CCCU members, Eastern Mennonite University and Goshen College, both announced in July that going forward they will accept married gay faculty, reversing a previous policy that had accepted only faculty who were either celibate or in a heterosexual marriage.

The two schools are the first of CCCU’s 100+ member schools to accept gay marriage, and some members have called for the two schools to be expelled over the matter, arguing they have rejected a pledge to be “Christ-centered and rooted in the historic Christian faith.” But thus far, CCCU has delayed, and Union president Dub Oliver says that’s simply unacceptable.

“Our advocacy for Christ-centered higher education means that we must stand with institutions that share our commitments. Regrettably, that is no longer the case with the CCCU,” Oliver wrote in an open letter to CCCU president Shirly Hoogstra. Eastern Mennonite and Goshen, he said, “abandoned fidelity to God’s Word when they endorsed same-sex marriage.”

Union may not be the last school to secede. Two weeks ago, Oliver said he believed as many as 40 schools may break away if CCCU refuses to ban the recognition of gay marriage.

The policy isn’t purely one of religious purity. Union and several other schools are fearful the federal government may attempt to revoke their tax-exempt statues based on their policies concerning sexuality. If Union is going to stand up to such a possibility, it wants to ensure unanimity among its allies.

“The fact that this is not unanimous damages our witness,” Oliver said in his letter to CCCU. “The reason we are passionate about this is because what we are talking about is not a secondary or tertiary theological issue — marriage is at the heart of the Gospel. To deny the Bible’s concept of marriage is to deny the authority of Scripture.”

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