Monte Carlo simulations of the critical region of the restricted primitive model are reported. Using mixed-field finite size scaling analysis we show that the critical behavior is compatible with Ising like behavior although due to statistical error on the simulation data and large correction-to-scaling contributions mean-field behavior cannot be totally excluded. With the assumption of Ising criticality the critical temperature is estimated to be 0.0488±0.0002 and the critical density 0.080±0.005.