A council is to ask all public bodies it deals with not to "discriminate" against parents who do not live with their children.
Cardiff council will now write to all other local authorities in Wales asking them to adopt the same principle.
Non-resident parents claim schools, hospitals and GPs' surgeries will often give information only to parents living with children
The number of single-parent households has risen yearly in Wales since 1991.
In 2007, the Welsh Assembly Government issued guidance to schools on how to deal with separated or divorced parents.