Basically, employers aren't supposed to hire people as independent contractors (1099) and treat them like employees by doing things like requiring them to work

Basically, employers aren't supposed to hire people as independent contractors (1099) and treat them like employees by doing things like requiring them to work specific hours, supplying their equipment, or giving them a semi-permanent position. The IRS views that as misclassifying employees to avoid paying their share of the social security and medicare taxes, which get foisted onto the contractor in the form of the self-employment tax.