A dynamical phase transition from integrability to non-integrability for a family of 2-D Hamiltonian mappings whose angle, θ , diverges in the limit of vanishingly action, I, is characterised. The mappings are described by two parameters: (i) , controlling the transition from integrable ( = 0) to non-integrable ( = 0); and (ii) γ , denoting the power of the action in the equation which defines the angle. We prove the average action is scaling invariant with respect to either or n and obtain a scaling law for the three critical exponents.