Enforced collection by the IRS includes levy of bank accounts, wage garnishments, and seizure of property to apply against your delinquent taxes. It contrasts to voluntary action you agree to take, e.g., paying your tax or making installment payments.
The IRS normally contacts you to discuss how you might pay your taxes or the matter resolved before using enforced collection. When a taxpayer does not respond to the IRS, e.g., by filing an unfiled return and or providing financial information, the IRS finds enforced collection effective in getting a response or collecting the taxes.
After the IRS starts enforced collection, it may agree to stop, e.g., if you provide requested financial information and enter into an installment agreement.