If you owe a tax debt to the IRS, they can take a big chunk of your wages, and it doesn't have to get a court order first. The amount you get to keep depends on how many dependents you have and your standard deduction amount. Your employer will pay you a fairly low minimum amount each week and give the rest to the IRS.
A wage garnishment is when the IRS requires your employer to withhold a certain amount of your paycheck and send it directly to them, until your debt is paid off. The IRS must send a wage levy notice to your employer, who is required to give you a copy. The notice includes an exemption claim form, which you should complete and return.