Are there other actions/substances for which states have opposed federal law?

Civil rights and desegregation come to mind.

abortion and speed limits

Faith-based abstinence-only sex education?

Slavery was abolished by states North of the Mason and Dixon line. A few states opposed DOMA, the so-called “defense of marriage act.” They oppose health care reform. Some states oppose federal regulation of payday lending.

The National Consortium of State Legislatures might give you more information. It seems to happen all the time.

States and the feds have clashed about alcohol many times. A few states were against the minimum drinking age. Vermont has even been considering lowering the drinking age to 18 in the past few years and other states were considering less radical steps (not that 18+ drinking is “radical”).

A state’s drinking age of 18 would not be a violation of Federal law.

However, the Federal government will withhold highway funds from states with a drinking age below 21.

So technically there is no law to oppose, but every state has chosen to keep the money and have a 21-year minimum age to purchase booze.

National Minimum Drinking Age Act of 1984

He asked if they opposed, not if they violate. The federal government probably can’t constitutionally mandate a drinking age, though it can control its own purse – so it’s definitely doing an end run around states’ rights. A good case can be made that it’s a constitutional overreach, and SCOTUS’ recent ObamaCare decision segues in that direction.

That said, a few states have sued over the matter.