Massachusetts Attorney General Maura Healey is among 21 state attorneys general that have sent a letter to the Consumer Financial Protection Bureau, urging the agency not to adopt recently proposed policies, saying that they say would erode critical consumer protections.

The policies include the CFPB’s use of no-action letters, or informal guidance provided by a federal agency stating that it does not intend to bring an enforcement proceeding based on facts described in an application.

No-action letters are typically non-binding and can be revoked at any time, but under the new CFPB proposal, no-action letters would no longer be non-binding staff guidance, would be of unlimited duration and could only be revoked under limited circumstances, according to the letter.

The policies also include the creation of a regulatory “sandbox,” a concept highly favored in the fintech industry that would allow financial services companies to test products without being subject to usual regulatory and licensing requirements.

Under the proposed sandbox policy, approvals or exemptions granted by the CFPB would grant the recipient immunity not only from a CFPB enforcement action, but also from enforcement actions by any federal or state authorities, as well as from lawsuits brought by private parties.

“The CFPB was created to protect consumers and ensure the financial stability of this country,” New York Attorney General Letitia James said in a statement. “These proposed rule changes would have the complete opposite effect – putting blind faith in the very industries and services they are supposed to regulate and correct. At a time when so many Americans are struggling to make ends meet, the CFPB should be focused on protecting consumers, not advancing regulations that could hurt them.”

Among many reasons, the state attorneys general objected to the CFPB’s proposed changes to its no-action letter because the effect of the changes would appear to make no-action letters binding on the CFPB indefinitely.

The attorneys general are also concerned because the proposal to streamline the application process by committing to issue no-action letters within 60 days of receipt could result in the CFPB making decisions hastily and without access to the data necessary to make an informed decision.

The states’ attorneys general objected to the sandbox policy on many of the same grounds.

They say there was no statutory authority for the CFPB to confer anything approximating the sweeping and absolute immunity of the type proposed.