The rule was meant to enforce an idea that might sound obvious: Retirement advisers have to act in the best interests of their customers.

On Friday, President Trump took a step toward halting it.

It's known as the fiduciary rule. It would have prohibited retirement advisers from accepting incentives for promoting certain funds over others. That can create a conflict of interest -- and advisers don't always have to disclose the incentives to clients.

The incentives can include cash and even vacations, according to Michael Spellacy, global wealth management leader at PwC. A 2011 study found that advisers recommend the fund that pays them more about half the time.

"Without this rule, customers are taking products that are very expensive from advisers who are incentivized for those products," Spellacy said.

The rule was unveiled last year by the Obama administration, but wasn't set to go into effect until April.

Proponents of the rule argued it was necessary to protect investors from abusive practices. The Consumer Federation of America said in a statement Friday that rolling it back would hurt the middle class.

"Brokers and insurance agents will be free to go back to putting their own financial interests ahead of the interests of their clients, recommending investments that are profitable for the firm but not the customer," the consumer group said. "And they will be permitted to do all this while claiming to act as trusted advisers."

Trump signed an executive order calling for the Labor Department to review the fiduciary duty rule.

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The change comes at an important time. Saving for retirement has become a major hurdle for Americans as pensions become extinct and the responsibility falls more heavily on individuals' shoulders. Many Americans turn to retirement advisers for advice to help build up their nest eggs.

Opponents of the rule argued that it went too far and would make retirement advice more expensive, which would ultimately hurt savers. Gary Cohn, director of the White House National Economic Council, said Friday that the rule "was completely misintended" and limited investors' choices.

"When you're trying to encourage younger and younger people to invest for a long period of time, you need to give them the proper choices that will allow them to accumulate wealth for a long period of time," he said in an interview on CNBC. "Don't limit people's choices -- give them the proper choices to accumulate wealth."

The Chamber of Commerce filed a legal challenge to the rule last summer claiming it would make it harder for advisers to provide financial advice.

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"The flawed fiduciary rule's rushed implementation would have jeopardized access to retirement advice and choice while its severe consequences and compliance burdens would have made it harder for small businesses to offer retirement plans," the chamber's President and CEO Thomas Donohue said Friday

But Spellacy noted that the wealth management business is highly profitable, and any changes could hurt profitability.

"When Dracula is guarding the blood bank, you expect him to try and make sure nothing changes," he said.

--CNNMoney's Heather Long contributed to this report.