Guidelines around the number of nurses in rest homes are potentially not being met around the country.

The Aged Care Association said most of its members provide the right number of hours of care from registered nurses.

A certain number of nurse hours per person is recommended in aged care, depending on the health and complexity of the person.

The Nurses Organisation says rest homes routinely don't meet the recommended number of nurse hours.

The union said often during reviews they find providers have a higher than recommended number of care giver hours, but a lower number of nurse hours.

Nurses' Organisation aged care advisor David Wait said this matters, because nurses are trained to a higher level of care.

He said it's those living in rest homes who miss out.

"They're the people that ultimately are really suffering from this. They're the ones not having the number of nursing homes that they really need.That can be mean issues don't get picked up in a timely way."

Chief executive of the Aged Care Association Simon Wallace said most but not all of their members meet these guidelines.

"We are an industry that is heavily audited, well regulated, as we should be for the vulnerability of the clients and we are delivering a really good quality of care," she said.

A certain number of hours of care from a registered nurse is recommended in aged care, depending on the health and complexity of the person.

Wallace said the sector is highly regulated and provides quality care.

"Members of the aged care association are largely meeting those recommended hours but the real key here is around the safe delivery of care."

The revelation comes the same week as a Waikato nursing home was fined for leaving a 92-year-old in a urine soaked bed.