Adair v.
United States, 208 U.S. 161 (1908)
The SCOTUS struck down a provision of the 1898 Erdman Act which would have prohibited railroads from requiring workers to agree not to join a labor union. (The Court addressed what "commerce" even meant.)
EDIT: The Court (in apparent response to FDR's heavy handed Court packing scheme) later reversed itself on the Adair case.
Bailey v.
Drexel Furniture, 1922
The SCOTUS voided the 1919 federal law that levied a big ass tax on products produced by child labor.
It was a cool decision that you would be well to review since it addresses the NECESSITY of voiding Unconstitutional legislation and cites yet other cases (including at least one other alleged "commerce cause" -based Act):
It is the high duty and function of this court in cases regularly brought to its bar to decline to recognize or enforce seeming laws of Congress, dealing with subjects not intrusted to Congress, but left or committed by the supreme law of the land to the control of the states. We cannot avoid the duty, even though it require us to refuse to give effect to legislation designed to promote the highest good. The good sought in unconstitutional legislation is an insidious feature, because it leads citizens and legislators of good purpose to promote it, without thought of the serious breach it will make in the ark of our covenant, or the harm which will come from breaking down recognized standards. In the maintenance of local self-government, on the one hand, and the national power, on the other, our country has been able to endure and prosper for near a century and a half.
Id. Words to remember.
Then of course, in Retirement Board v. Alton Railroad Co., striking down yet another Act allegedly premised on the Commerce Clause authority, the SCOTUS also voided the Railroad Retirement Act.
RAILROAD RETIREMENT BOARD v.
ALTON R. CO., 295 U.S. 330 (1935).
So much for "unprecedented."