PO net price updation with respect to contract net price change

We have a requirement: Whenever net price in Contract is changed, net price in open purchase orders (for which GR has been not done yet) which are created with reference to that contract updated automatically.

For example net price in a conract is 13 USD and there are 5 open POs. now net price (PB00) in contact is changed to 13.5 USD without changing the condition validity date, then it should be automatically updated in those 5 POs.