Wall Street's industry-funded watchdog will evaluate disclosures of securities firms in light of a new U.S. Labor Department retirement advice rule requiring them to act in customers' best interests, the regulator's chief said on Thursday.

The Financial Industry Regulatory Authority will look at whether actions by securities brokers who give retirement advice are in synch with what they tell clients in so-called "best-interest contracts" required by the Labor Department rule, said Richard Ketchum, Finra chairman and chief executive.

Finra does not have authority to enforce the Labor Department rule, Ketchum said. "But we do have the authority to look and see whether firms are dealing fairly with their customers and not misleading their customers," Ketchum said at the Reuters Global Wealth Summit in New York.

In April, the Labor Department released a rule for brokers who sell retirement products, including Individual Retirement Accounts.

The rule, which takes full effect in 2018, will require brokers who give retirement account advice to become "fiduciaries" and act in clients' best interests, instead of choosing products that line brokers' own pockets.

The rule followed a years-long clash involving multiple industry groups and lawmakers. They argued that the new requirement will drive up costs and make it impractical for them to manage money for small investors.

Ketchum said he believes the Labor Department does not have enforcement authority over IRAs. Industry groups made a similar argument, among others, in a lawsuit filed June 2 in a U.S. District Court in Texas to challenge the rule. Ketchum made no comment on that lawsuit.

Nonetheless, securities industry rules require that firms live up to representations they make in disclosures. Those representations would include written statements to customers that firms will act in clients' best interests to satisfy the Labor Department rule, Ketchum said.

Finra will also follow changes firms may make to investment strategies in response to the rule, he said. Those changes may be justified, but companies will still have to justify their reasons.

"Firms should be thinking about showing their work," Ketchum said.