The DOL rule will require any advisor or provider to a plan with less than $50 million in assets, and all brokers and advisors to IRA accounts, to act as fiduciaries.

Advisors and brokers selling investment products on commission are expected to have to do so under the rule's Best Interest Contract Exemption. And any recommendation to roll over 401(k) plans assets to an IRA will be considered a fiduciary act. Advisors will be able to operate outside the BIC exemption on rollovers if they charge a fee level to what were charged the assets while in 401(k) plans.

Section 913 of the Dodd Frank Act, which President Obama signed into law in July 2010, gave the SEC authority to adopt a uniform fiduciary standard for all broker-dealers and advisers giving investment advice or selling investment products.

In November of last year, Sec Chair Mary Jo White told a Congressional hearing of her intent to make a new investment standard a part of the agency's rulemaking agenda.

"The differences in the standards that apply to advice under the federal securities laws has led me to conclude that broker-dealers and investment advisers should be subject to a uniform fiduciary standard of conduct when providing personalized investment advice about securities to retail investors," White told a House committee hearing last year.

Chair White's term is scheduled to end in 2019. But it is unclear if she will serve the entirety of that term. Four chairpersons have served truncated terms since 2000.

Two of four commissioner seats are currently vacated, but the two prospective replacements were recently approved in a Senate committee hearing vote.

Once the SEC crafts a new investment standard, White will need the support of at least two other commissioners to see the rule through.

During congressional hearings, several lawmakers have voiced concern over whether a new SEC advisor standard could function in accord with the DOL fiduciary rule.