New consumer protections requiring financial advisers to put their customers’ interests ahead of their own — at least when handling their retirement money — will take effect next month, putting to rest the question of whether they would be delayed further.

The fate of the so-called fiduciary rule, created under the Obama administration, was called into doubt when President Trump signed an executive order seeking a review of it, prompting regulators to delay its implementation to June from April. On Tuesday, Alexander Acosta, the Labor Department secretary, said the basic principles of the rule would indeed take effect on June 9, even as his agency continues to review its finer details.

After careful review, the Labor Department has “found no principled legal basis to change the June 9 date while we seek public input,” Mr. Acosta wrote in an opinion piece published Monday in The Wall Street Journal. “Respect for the rule of law leads us to the conclusion that this date cannot be postponed.”

The Obama administration had estimated that conflicts of interest embedded in the way many investment professionals do business cost Americans about $17 billion a year, producing annual returns that are about 1 percentage point lower.