Starting this fall, the big three credit reporting agencies — Equifax, Experian, and TransUnion — will be required to let you freeze your credit file for free. A freeze can help prevent identity thieves from applying for credit cards, opening bank accounts or taking out loans in your name.

Congress mandated free freezes in response to consumer outrage over the Equifax breach last September that exposed the personal information of more than 146 million Americans.

The free-freeze provision was included in a banking deregulation bill signed by President Donald Trump last month that rolled back some of the reforms put into place by the Dodd-Frank Act in 2010 after the Great Recession.

Consumer groups blasted the rollback of the Dodd-Frank protections less than 10 years after the economic meltdown, even as they praised Congress for making credit freezes free.

Some states require a free freeze. For the rest, it can cost as much as $10 to freeze or unfreeze (thaw) a file, depending on where you live.

Note: Equifax will freeze your file for free until June 30. The company made this offer following last year’s mega-breach.

“This is good news; this is a move in the right direction,” said Eva Velasquez, president and CEO of the non-profit Identity Theft Resource Center. “The ability to avail yourself of one of the strongest proactive steps you can take to minimize your risk of identity theft is finally free for all Americans — not just those 65 and older or those who reside in a certain state or those who have already been victims of identity theft.”

And yet, there are some concerns about the new law.

“It preempts and replaces stronger state freeze laws with a weaker national one,” said Mike Litt, consumer campaign director for the consumer advocacy group U.S. PIRG. “The protection offered through a credit freeze in many states will be weakened, and individual states are now prohibited from improving the freeze for their own residents.”

At Consumers Union (the advocacy division of Consumer Reports), Anna Laitin, director of financial policy, is also worried about the negative consequences.

“States have been the innovators on credit freezes, and this legislation would stop that innovation in its tracks,” Laitin said in a blog post. She points to a bill before the California legislature that would speed up and simplify the process.

S.B. 823 would require credit reporting agencies operating in the state to freeze, temporarily lift or remove a security freeze received by mail within one business day instead of the current three days. This would need to be done within 15 minutes of authenticating a request via the internet or a mobile device.

What happens next?

Provisions of the new federal credit freeze law take effect in late September. This will give the credit reporting agencies time to update their websites to make it easy for you to request a free credit freeze or thaw.

The new legislation requires the credit bureaus to freeze an account within one business day of a request made online or over the phone and within three business days when notified by mail. An account must be thawed within one hour of a verified request by phone or online and within three business days after receiving a request by mail.

For full protection, you will need to request a freeze at each of the three big credit reporting agencies. If you’ve already done that, you’re all set. Once the law takes effect, you will be able to thaw the account and refreeze it at no cost — something you’ll need to do if you apply for credit.

Note: A freeze does not affect your relationship with current creditors and it does not impact your credit score.

Two of the big credit bureaus, Transunion (TrueIdentity)and Equifax (Lock & Alert) offer free services that let you “lock” your credit file from a computer or mobile app. You can “unlock” your account in seconds, if you want to open it to a potential creditor. You’ll receive an instant alert any time your file is locked or opened.

A credit lock is like a security freeze in many ways, but it’s not regulated by federal law. With a freeze, you must use a PIN to identify yourself. With a lock you can use an email and password or in some cases, a fingerprint or facial recognition.

Some consumer advocates believe a freeze is preferable because it’s guaranteed by law, but all agree a lock is better than leaving your file wide open.

“I realize that convenience is important and the process of locking your account may be slightly more simplified than freezing it,” Velazquez told NBC News. “But the reality is the credit freeze is not that cumbersome and soon the cost will not be an issue for people. So now consumers simply need to evaluate which one of these security measures is appropriate for me.”

Fraud experts tell NBC News everyone should assume their Social Security number has been hacked and is available for sale on the black market. That means everyone needs to protect their credit file.

A freeze cannot prevent all identity theft

Credit monitoring can alert you to a problem, but it doesn’t stop the crime.

A freeze — or lock — is one of the few proactive steps you can take to reduce your risk of becoming a victim of financial identity theft. Blocking new creditors from reviewing your credit report makes it tough for crooks to get credit in your name — whether that’s a car loan or a new credit card.

Keep in mind: A locked or frozen credit file does not stop other forms of ID theft. Armed with your Social Security number and birthdate, a thief can still file a bogus tax return in your name, steal your health benefits, apply for a job or get a driver’s license in your name.

Herb Weisbaum is The ConsumerMan. Follow him on Facebook and Twitter or visit The ConsumerMan website.