I am trying to use the Mann-Whitney U Test to compare ordinal data between 2 groups, but the problem is that there are only 3 categories for my ordinal data. I have never seen the Mann-Whitney U Test be used on ordinal data with fewer than 5 categories. So I was wondering, what is the minimum number of categories in order for Mann-Whitney U Test to be used?

Any input would be much appreciated. Thank you!!