People seeking compensation over mis-sold PPI will have to make a complaint before a deadline set in August 2019, the City regulator has said.
The Financial Conduct Authority (FCA) said it will start a two-year communications campaign from August 2017 to alert consumers to the cut-off point drawing a line under the scandal.
The watchdog said consumers who intend to complain about payment protection insurance "should do so as soon as possible".
They should continue to complain to the firms concerned and to the Financial Ombudsman Service if they are not satisfied with the response.
Consumers have until August 29 2019 at the latest to make their complaint, but some, including those who have previously been told by their firm that they may have been mis-sold, may run out of time sooner, the FCA said.
Making a complaint is free and most people should not need to use a claims management company, which could take a chunk of any payout, to help them.
Andrew Bailey, chief executive of the FCA, said: "Putting in place a deadline and campaign will mean people who were potentially mis-sold PPI will be prompted to take action rather than put it off. We believe that two years is a reasonable time for consumers to decide whether they wish to make a complaint.
"We have carefully considered the feedback we received and we still believe that introducing a deadline for PPI complaints and a communications campaign warning of the deadline will benefit consumers."
According to the FCA's figures, a total of £26.2 billion has already been paid out since January 2011 as a result of the PPI scandal.
PPI was often tacked onto other financial agreements, such as store cards, without consumers wanting or needing it.
Consumer group Which? said the major banks alone have set aside more than £35 billion to pay PPI compensation.
Vickie Sheriff, Which? director of campaigns and communications, said: "It's been clear for years that the banks should be working much harder to resolve PPI claims fairly.
"The current process has been wholly inadequate and driven too many consumers to use claims management companies.
"Now the regulator has confirmed a deadline for the victims of this mis-selling scandal to make a claim, it must ensure that banks are doing much more to help customers get back the money they are owed."
Figures released by the financial ombudsman this week showed that PPI continues to make up just over half of the complaints it receives.
Chief ombudsman Caroline Wayman said earlier this week that while PPI complaints had recently drifted downwards, "there are some suggestions that this could be the calm before the storm".
She said the PPI deadline could heavily influence the ombudsman's complaints volumes.
Martin Lewis, founder of MoneySavingExpert.com - which like Which? has free help with PPI claims on its website, said: "The deadline is a mistake. The stats are plain. Flabbergastingly, in over half of all cases where after the bank rejects a PPI reclaim people take it to the independent ombudsman, the bank's rejection is overturned.
"Until we can trust banks to deal with complaints fairly in the first instance, this move to protect their balance sheets should not happen. It is putting the protection of the financial industry ahead of consumers."
Mr Lewis also predicted the deadline would prompt an upswing in spam PPI calls as claims firms try to cash in.
Urging consumers to act themselves, he said: "PPI was systemically mis-sold on loans, credit and store cards, and commonly mis-sold on mortgages and overdrafts.
"If you've had one of those in the last 20 years, check if you've got the paperwork, and if so if it had PPI on it.
"And ensure you reclaim for free - there's lots of help out there, you don't need to pay someone."