John Patten, the former Secretary of State for Education, is poised to lead Tory backbench opposition to the proposals by the Lord Chancellor to simplify the laws on divorce.
Mr Patten, a leading Roman Catholic, has urged the Government to "bury the Bill" before it buries marriage. He could be an important champion against the Bill, which is scheduled to be introduced in the next Queen's Speech in November.
The Government has anticipated trouble with its own backbenchers by announcing that it will allow a free vote on the measure, allowing MPs to vote against it with impunity.
Mr Patten is understood to have opposed the proposals with John Redwood, the former Secretary of State for Wales, when they were mooted in the Cabinet. The Bill is likely to cause anxiety for other committed Christians in the Government, including John Gummer, Secretary of State for the Environment, and Ann Widdecombe, the Home Office minister.
Mr Patten called for a Royal Commission on divorce, and for the Bill to be subjected to the special procedure in which expert evidence can be taken in committee. "But best of all, if it were quietly buried before the Bill buries the institution it seeks to reform," he said on BBC Radio.
He said the measure would enable husbands and wives to demand divorce a year after marrying, even where there was no evidence of the marriage having irretrievably broken down.