Support in Parliament for plans to introduce no-fault divorce are "disappointing", the Coalition for Marriage has said.
The Divorce, Dissolution and Separation Bill seeks to make it easier for couples to divorce by removing the requirement for partners in a marriage to find "fault", such as adultery or dissertion.
Alternatively, couples must live separately for at least two years before beginning divorce proceedings.
Further changes introduced by the Bill would remove the right of a partner to contest the divorce.
The reforms could see divorces granted in as little as six months.
The proposals were backed by MPs in the Bill's second reading in Parliament last week. A Public Bill Committee is to take oral evidence on Tuesday.
The Coalition for Marriage said MPs have "misguidedly" given their backing to no-fault divorce and called the Bill a "marriage-wreckers' charter".
Claims by Paul Maynard MP during the debate that the Bill would not make divorce quicker, easier or more commonplace were "astonishing and irresponsible", it said, adding that scrapping the basis of fault would abolish all differences in divorce between traditional marriage and same-sex marriage.
"That's more divorces, more quickly," it said.
"The parliamentary process is only just beginning. We will seek opportunities to amend it. Any ministerial changes following the election of a new leader of the Conservatives may also have an impact."
Conservative MP Fiona Bruce said during the debate that the Bill might lead to a decrease in the number of young people choosing to marry.
"I am concerned that, if marriage can be seen as so easily exited, more and more young people will think, 'Why bother entering into it at all?'" she said.
"Marriage rates may well, and likely will, further decline."
She said the changes would also diminish the likelihood of couples seeking to reconcile with one another.
"I think these proposals will do even less than current procedures to help to promote dialogue and potentially therefore reconciliation," she said.
"Currently, each year, approximately 10,000 divorces are started and then dropped. Many couples do give their marriage another chance.
"However, these proposals—in effect, promoting unilateral divorce on demand simply by serving a notice on the other person that the marriage has broken down, without having to give any reason at all and without the spouse being able to contest this should they want to—will, I believe, inhibit the dialogue that could promote reconciliation in some cases."