Upvote:7
Normal mustard is a liquid. It can be transported in hold luggage, the luggage you hand in before the flight.
But if in hand luggage, the bag you take in the plane yourself, it can only be in small amounts and in your liquids bag.
That is maximum containers of 3.4 oz, (3 oz is the safe amount) and all of the containers have to be in the one quart plastic (ziplock) bag.
(That is 100ml for the individual containers and a one liter bag, for those who are metric.)
See the rules on the TSA website here.
Mustard is about in the same range of fluidity as toothpaste, I think.
Only powdered mustard can be transported in hand luggage in bigger amounts.
As noted in the comment on the question, food items can be a problem when crossing national and sometimes already state boundaries. You will have to tell the customs people that you transport food and if unlucky you will have to leave it behind, as not allowed. (I can not be sure whether it is allowed or not.)