Is there a law or rule that (indirectly?) requires the letter grading system? I considered going to a college that used a non-linear grading system: you’d rece

Is there a law or rule that (indirectly?) requires the letter grading system? I considered going to a college that used a non-linear grading system: you’d receive an in depth essay explaining your strengths and weaknesses. They would still create a standard lettered grade, but they would not give it to you unless you asked, and they advised you not to ask. It was implied they needed to create the lettered grade to comply with some regulation - possible to show there was no racial bias? Not sure.