We have some discontinuities in our tax code in Argentina, if you are an independent worker, and earn up to 11,916,410 pesos ($11,682) per year, you pay 793,332 pesos ($777) in taxes, around 6.6%, but if you earn one more peso, you enter the general regime, and start paying >50% in taxes.
A simple solution (probably used in many places) to this problem is to have brackets. Everybody is taxed 6.6% on its income until a certain threshold and the rest is taxed at 50%. You can add more brackets as needed. And so, there is no incentive to be just bellow a certain bracket threshold.
