The executive branch can check the other branches of government through its power to veto legislation passed by the legislative branch. If the president vetoes a bill, it cannot become law unless the veto is overridden by a two-thirds vote in both the House and the Senate. The executive branch can also check the legislative branch by refusing to sign appropriations bills, which would prevent the government from operating. Additionally, the executive branch can challenge the constitutionality of laws passed by the legislative branch by appealing to the judicial branch. Finally, the executive branch can check the judicial branch by refusing to enforce court orders, although this is a rare occurrence.