National coordinator for First Union, Ben Peterson, told RNZ that New Zealand's "she'll be right" attitude is an issue, particularly in a pandemic.
"Every day this is an occurrence, that people are trying to use their sick leave and they're told just to come in anyway."
Peterson said short-staffing in retail and other industries leads to subtle pressures on workers not to use their entitled sick leave.
In front-facing roles it's really important that people are fit to work to protect everyone they are coming in contact with, he said.
"Sick leave is something that's there to protect workers and there to protect everyone.
"The Covid situation shows that it's not a nice-to-have, this is something we need to have in place, we need to have robust systems so people can use sick leave when they need it."