(CNN) United Methodist churches and clergy could face removal from the denomination if they do not affirm its stance against gay marriage and noncelibate LGBT clergy by 2021. The church reached the decision in a vote at a General Conference in St. Louis on Tuesday.

Church leaders say the move will almost surely lead more liberal members to leave the mainline denomination.

The vote for the "Traditional" plan came after the church voted to reject an earlier proposal, known as the "One Church" plan, which would have allowed local churches to perform same-sex weddings and hire openly LGBT clergy. That move was pitched by proponents as a way to keep the increasingly fractious denomination together amid widespread disagreements about scripture and the morality of same-sex relationships.

"Many of us have members who are saying they will leave," said the Rev. Tom Berlin of Virginia, a member of the church's legislative committee. "A virus of conflict will spread."

Instead, United Methodists voted to push forward the "Traditional" plan, which passed with a vote of 438 to 384.

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