In a giant step forward for investor protection, the Department of Labor proposed new rules this week to ensure that financial advisers act solely in their clients’ best interests when giving advice and selling products for retirement accounts. The new standard of fiduciary duty would bar stockbrokers, insurance agents and other financial professionals from increasing their pay by steering clients into high-cost products and strategies when comparable lower-cost ones are available.

For Labor Department officials, the challenge now is to see the proposal through the rest of the rule-making process. The United States Chamber of Commerce, which has opposed the fiduciary standard, has already said it plans to ask for an extension of the 75-day comment period. Other delay tactics are all but certain.

The opponents are fighting for a status quo in which retirement savers pay an estimated $17 billion a year in excess fees and commissions to advisers who steer them into needlessly high-cost investments because they have no obligation to put the client first. They say that imposing a fiduciary duty on retirement advisers will upend commission-based business models that are more affordable for small savers than arrangements that charge a flat fee based on the size of the retirement portfolio.

But the proposed rules address that concern by allowing commissions and transaction-based fees as long as the adviser and the firm meet certain criteria. They must acknowledge their fiduciary duty in a written contract with the client. Fees must be in line with industry norms. A firm’s policies cannot be at odds with the adviser’s fiduciary duty; for example, the firm cannot run contests that would give the advisers an incentive to steer the clients into higher cost investments. The proposed rules put forward the kinds of assets that commission-based advisers can recommend and those that would be off limits because of their high fees, risks and complexity.

The new rules would apply to advice about rolling over a 401(k) plan into an Individual Retirement Account, which for many savers is the biggest financial decision in retirement. They also sensibly specify that advice is advice no matter who gives it. Mutual funds had lobbied for exempting call center employees from the proposed new rules, but the proposal has no blanket exemption. It makes clear that general education does not involve a fiduciary duty, but individualized advice does.

Secretary of Labor Thomas Perez and his team deserve praise for a well-crafted proposal. Now they need to carefully vet the public comments and promptly issue a final rule that preserves the proposal’s strong protections for retirement savers.