Laws regarding the legality of butterfly knives (also known as balisongs or Batangas knives) vary from state to state in the U.S. Some states prohibit them outright, while others have restrictions based on blade length or other factors.

Here are a few examples of states where butterfly knives were considered illegal or restricted as of 2021:

1. Hawaii: Possessing, selling, transferring, or manufacturing a butterfly knife is illegal.
2. California: Butterfly knives are legal to own, but are illegal if the blade is longer than 2 inches.
3. New York: The law is ambiguous as it prohibits any "gravity knife", which could potentially include butterfly knives.
4. Washington: Butterfly knives are classified as spring blade knives and are therefore illegal.
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It's important to note that laws can change, and local ordinances can also impact the legality of possessing such a knife. Always refer to the current laws in your specific location, and consider consulting with a legal professional if you have questions.