Regulators do not prohibit auditors from providing tax services to their audit clients, provided that these services are preapproved by audit committees. I examine whether the association between auditor-provided tax services and earnings management in tax expense varies with audit committee effectiveness. I develop a composite proxy for audit committee effectiveness by combining six audit committee characteristics. I find that auditor-provided tax services are less positively associated with earnings management in tax expense as audit committee effectiveness increases. My findings suggest that the knowledge spillover effect of auditor-provided tax services is more likely to dominate the independence impairment effect when auditor-provided tax services are preapproved by more effective audit committees.