Assistance in collection of taxes: mutual enforcement and conservatory measures apply under recipient State's domestic law. Article 28A obliges Contracting States to assist one another in collecting revenue claims, permitting a competent authority to request that enforceable claims or claims subject to conservatory measures be accepted for collection or conservancy by the other State, which shall apply its own laws as if the claim were its own. Assistance is constrained: accepted claims are not subject to the recipient State's time limits or given priority under the requesting State's law; disputes over existence, validity or amount cannot be litigated in the assisting State; and assistance may be refused where measures would contravene domestic law or public policy, reasonable collection efforts have not been pursued, or the administrative burden is disproportionate.