They can't MAKE you do anything, but they will try to guilt trip you. If you're sick -you're sick. it doesn't matter if you're off 1 day or a week as long as you call them and let them know at least 2 hours before your shift. It's a good idea to get a doctor's note though.
__________________
Would you like fries with th... I mean, your milk in a bag?
With the usual "May vary based on manager/store/district/division/contract/state" disclaimer...
With our contract, you only need a doctor's note if you've missed three consecutive days off. There's a Union poster in the break room loudly proclaiming this rule. This in no way stops management from guilt-tripping and haranguing and threatening you with write-ups for not having a doctor's note for even two days.