The Families Secretary Ed Balls and his Conservative shadow, David Willetts, have been outlining the policies for families.
Speaking on this morning's programme, Mr Willetts said that he believed the tax system should recognise marriage. But he added that this would be a commitment for the lifetime of a parliament should the Conservatives form the next government and would be "unlikely" to feature in its first budget.
Mr Balls criticised the Conservative pledge, saying that it would mean that divorced or widowed people, or those whose partners had left following domestic violence, would be "second-class and disadvantaged".
Both parties are outlining their family policies today. Mr Balls is expected to unveil a new guide for new fathers, while the Conservatives say that they will include a pledge to recruit an additional 4,200 health visitors in their general election manifesto.