the Sixteenth Amendment, which allows Congress to levy an income tax, comes into conflict with the Fifth Amendment, which includes a right against self-incrimination. The conclusion of the matter is unsurprising; it would be absurd to exempt criminals from reporting income on their tax
forms while asking it of honest workers. However, Fifth Amendment privilege allows one to report illegal income without revealing its precise source.
In the US you are famously required to report income from illegal sources on your taxes, which was famously Al Capone’s downfall