The controversy began when a Detroit area Catholic school displayed what it called a "modesty poncho". The poncho would be passed out at the doors entering the prom to girls wearing dresses that did not meet dress code requirements. The school has since backed off the idea.
Read The USA Today
https://www.usatoday.com/story/news/nation-now/2018/05/01/modesty-ponchos-prom/568491002/