Rule of Law

Enchantment

Each player can't cast more than one spell each turn.

2019-07-12:
Rule of Law looks at the entire turn to see if a player has cast a spell, even if Rule of Law wasn’t on the battlefield when that spell was cast. Notably, you can’t cast Rule of Law and then cast another spell during the same turn.
2019-07-12:
If you cast a spell that was countered, you can’t cast another spell during the same turn.