Nurses in England deserve to be paid the same as their Northern Ireland counterparts, their union has said.
The pay rise will be back-dated until 1 April
Earlier on Tuesday, NI Health Minister Michael McGimpsey said nurses would receive the full pay award recommended by the Independent Pay Review Body.
The move means that nurses and midwives will receive a 2.5% increase back-dated from 1 April.
Peter Carter, General Secretary of the Royal College of Nursing, said the situation was unjust.
"Nurses in England will still be left out in the cold because they continue to be offered a lower pay deal than their Celtic cousins," he said.
"A nurse giving care and saving lives in London should be as valued as a nurse in Cardiff, Belfast or Edinburgh.
"But, when it comes to nurses' pay, we have a Disunited Kingdom in which nurses working in England find themselves discriminated against."
Speaking earlier on Tuesday, Mr McGimpsey said all key workers in "the wider health service team" would get the increase.
The decision means that the only nurses in the UK who will not receive their full pay from April are those working in England.
They are getting 1.5% now and an extra 1% in the autumn.
Mr McGimpsey said he was on record as saying he believed that nurses "deserved to have their pay in full".
The minister said the pay rise would also be awarded to administrative and clerical staff "as well as other support services".
Mary Hines, Northern Ireland director of the Royal College of Nursing, said it was not just an investment in nurses, but also in patient care.
"The health minister has been very supportive, one has to say that Finance Minister Peter Robinson, who has to make difficult decisions, and the executive have been wonderful," she said.
"They have listened to the voice of nursing and nurses in Northern Ireland."
A Department of Health spokesman said decisions on implementation of pay were a devolved matter, and the Northern Ireland Assembly had decided on a course of action reflecting their own regional issues.
"The government has already announced the pay award for health professionals in England - a fair award reflecting the balance between the right level of pay and the need to be vigilant against the threats of inflation."