Slack Work is the largest component of Part-Time Employment for Economic Reasons. As you see here, the number has been little changed since early 2017. The question now is whether the spike we see in January is due to the adjustments that are made to the January numbers every year or whether it is a harbinger of something more ominous.
Slack work is the category the BLS uses to count persons who said they wanted to work full-time but were limited to 34 hours per week or less because their employer did not have enough for them to do beyond the hours they actually worked.
