I have argued (in my op-ed in the Dallas Morning News last year and elsewhere) that the Congress ought not waste time doing anything more than studying the issue of changing the number of justices on the U.S. Supreme Court (if FDR could not do in 1937, right after his historic landslide reelection with the enlargement of his party's majorities in both houses of Congress, then today the Democratic Party could not possibly hope to do so and should instead remain focused on solving urgent problems for the people).
Today I found a supporting authority:
"In 1937 President Roosevelt proposed a bill that would have authorized the appointment of an additional justice for each sitting justice over 70 years of age, up to a maximum of 15 justices. The bitter fight that led to the defeat of this “Court-packing” plan, as it was regarded, has given the notion of a nine-person Court such sanctity that it is unlikely that the size will ever be changed."
13 Wright, Miller & Cooper, Federal Practice & Procedure, Jurisdiction § 3507 (3d ed.) (emphasis added)