Currently negotiating an over-run modification on a CPFF delivery order. The over-run modification will also extend the PoP by 5 months. The contractor believes that a TINA Cert is not required IAW FAR 15.403-2b "Certified cost or pricing data are not required for proposals used solely for over-run funding or interim billing price adjustment". The Government believes since the modification is primarily for over-run funding but also includes the PoP extenstion, it is not solely for over-run funding and a TINA Cert is required. We are at a stand-still with negotiations so any help will be appreciated.