When the government or a business has a rule or law that might make it hard for some people to do things, or that might cost a lot of money, they need to make sure that it's still fair to all the people involved. One way they do this is by using something called the "undue burden standard."
This means that they have to ask themselves if the rule or law is really necessary and if there's any other way to do things that wouldn't be so hard or expensive for everyone. They have to think about how many people might be affected, how important the rule is, and if there's any way to make things easier without giving up what the rule is trying to do.
Basically, the "undue burden standard" tells the government and businesses that they need to be extra careful when making tough rules, so that they don't make things too difficult or unfair for people who might be affected by them.