Voluntary Compliance
“Voluntary compliance” is a phrase the IRS, congressional committees, and the courts use to describe the structure of the U.S. federal tax system. The system is “voluntary” in the technical sense that taxpayers compute their own liability and file returns reporting it, rather than receiving a pre-computed assessment from the government. The contrast is with countries where the tax authority issues each citizen a pre-filled bill that becomes due unless contested.
The phrase is unfortunate. It strongly implies optionality of the underlying obligation, which is not the case. The substantive duty to pay tax is created by statute (subtitle A of the Code), and failure to pay is criminally sanctioned under §7201 (evasion) and §7203 (willful failure to file).
The term is one of several places where the tax system describes itself in language that creates predictable confusion. The alternate-tax-theory community has built substantial argumentation on this confusion — most of it doctrinally unsupported, but resting on a real defect in how the system communicates with the public it taxes. The IRS would do well to retire the phrase.