As regulators have cracked down on auditor independence violations, the spread between what companies pay for the financial statement audit compared with other non-audit services performed by the same firm has grown to its greatest gap yet in the post Sarbanes-Oxley era.

According to the latest study by Audit Analytics of fees paid in 2014 by 2,300 accelerated filers, 80.3 percent were focused on the integrated financial statement internal control audit. Fees for non-audit services, including tax services that are allowed to be performed by the auditor under auditor independence rules, dipped to 19.7 percent of the total bill from the audit firm, a drop from a figure that has held fairly steady around 20 percent the past several years. Before Sarbanes-Oxley the split between audit and non-audit services was almost exactly 50-50.

When factoring in the effect of audit services that are more closely related to the audit, and fees related to that audit, such as employee benefit plan audits, due diligence for mergers or acquisitions, accounting consultations, internal control reviews, or attest services not required by regulation, the analysis finds 90.6 percent of the audit bill goes to audit and those related audit services compared to 9.4 percent in non-audit services. That’s also a marked different from recent years when 11 percent to 12 percent of teh bill went to non-audit services.

When factoring audit and audit-related fees against revenue, (to adjust for inflation and corporate growth from year to year) the analysis shows companies paid an extra $9 per million in revenue for audit services in 2014 compared with 2013. Companies in the research population paid $541 per million in revenue for their audit and audit-related services in 2013, and that rose to $550 per million in 2014.

The drop in non-audit fees paid by the same companies appears even more clearly when factored against revenue. Companies paid $57 per million in revenue in non-audit services in 2014, down from $69 per million in 2013, a drop of 18.8 percent, Audit Analytics says.

The Securities and Exchange Commission delivered enforcement actions against Deloitte, KPMG and EY since early 2014 to remind auditors that they are responsible for keeping tabs on their relationships with audit clients to assure non-audit business activities do not hamper their ability to deliver an independent, objective audit. The Public Company Accounting Oversight Board has delivered a string of enforcement actions as well, mostly focused on smaller firms or on auditors of broker-dealers.