A simple majority in the house and the senate is all that's required.
http://www.nytimes.com/2007/07/26/opinion/26smith.html?_r=2&oref=slogin&oref=sloginWHEN a majority of Supreme Court justices adopt a manifestly ideological agenda, it plunges the court into the vortex of American politics. If the Roberts court has entered voluntarily what Justice Felix Frankfurter once called the “political thicket,” it may require a political solution to set it straight.
When the court overreaches, the Constitution provides checks and balances. In 1805, after persistent political activity by Justice Samuel Chase, Congress responded with its power of impeachment. Chase was acquitted, but never again did he step across the line to mingle law and politics. After the Civil War, when a Republican Congress feared the court might tamper with Reconstruction in the South, it removed those questions from the court’s appellate jurisdiction.
But the method most frequently employed to bring the court to heel has been increasing or decreasing its membership. The size of the Supreme Court is not fixed by the Constitution. It is determined by Congress.
If the current five-man majority persists in thumbing its nose at popular values, the election of a Democratic president and Congress could provide a corrective. It requires only a majority vote in both houses to add a justice or two. Chief Justice John Roberts and his conservative colleagues might do well to bear in mind that the roll call of presidents who have used this option includes not just Roosevelt but also Adams, Jefferson, Jackson, Lincoln and Grant.