The U.S. government suddenly banned bakeries from slicing bread for their customers beginning in January, 1943. The reason was never clear. It was probably was an attempt to conserve wax paper, which sliced bread was wrapped in. Or maybe to save the steel used to make slicing machines. Sliced bread was also thought to spoil faster. Another possible reason: the government was trying to soften the blow of an increase in the price of wheat flour, since bakers could charge for slicing bread.
The ban was very unpopular and the government ended it two months later with a lame explanation that the savings had been less than anticipated.
See: “During World War II sliced bread was briefly banned in America” by Magda Origjanska on The Vintage News website (2017)