A growing literature documents that effective tax rates respond to changes in IRS enforcement capacity, interpreting this evidence as firms adjusting aggressive tax positions in response to changes in audit probability. This paper provides a direct test of that interpretation using FIN 48 disclosures of uncertain tax benefits, which capture firms' own assessments of which tax positions might not survive examination. Within the sample of UTB reporters, effective tax rates respond to audit rate changes in the direction prior work documents. In the same sample, however, none of four UTB-based measures of aggressive position adjustment shows any response. The ETR response is broadly distributed across sectors rather than concentrated in any single industry. This pattern is difficult to reconcile with a deterrence channel operating through recognized uncertain positions. The findings suggest that enforcement-induced tax planning operates through margins other than the disclosed uncertain-position channel.