What is the burden of proof in an action to collect tax?

In an action to collect tax, the government bears the burden of proof. The government can usually carry its initial burden, however, merely by introducing its assessment of tax due. Normally, a presumption of correctness attaches to the assessment, and its introduction establishes a prima facie case. Welch v. Helvering, 290 U.S. 111, 115, 54 S.Ct. 8, 9, 78 L.Ed. 212 (1933); United States v. Molitor, 337 F.2d 917, 922 (9th Cir.1964). The presumption does not arise unless it is supported by a minimal evidentiary foundation. Weimerskirch v. Commissioner, 596 F.2d 358, 360 (9th Cir.1979). The taxpayers contend that the assessments here were not entitled to the presumption of correctness because they lacked any factual foundation.