In this work we present a thorough analysis of the phase transitions that occur in a ferromagnetic 2D Ising model, with only nearest-neighbors interactions, in the framework of the Tsallis nonextensive statistics. We performed Monte Carlo simulations on square lattices with linear sizes L ranging from 32 up to 512. The statistical weight of the Metropolis algorithm was changed according to the nonextensive statistics. Discontinuities in the m(T) curve are observed for q ≤ 0.5. However, we have verified only one peak on the energy histograms at the critical temperatures, indicating the occurrence of continuous phase transitions. For the 0.5 < q ≤ 1.0 regime, we have found continuous phase transitions between the ordered and the disordered phases, and determined the critical exponents via finite-size scaling. We verified that the critical exponents α, β and γ depend on the entropic index q in the range 0.5 < q ≤ 1.0 in the form α(q) = (10 q 2 − 33 q + 23)/20, β(q) = (2 q − 1)/8 and γ(q) = (q 2 − q + 7)/4. On the other hand, the critical exponent ν does not depend on q. This suggests a violation of the scaling relations 2 β + γ = d ν and α + 2 β + γ = 2 and a nonuniversality of the critical exponents along the ferro-paramagnetic frontier.