People who receive tax credits have just one week left to tell HM Revenue & Customs (HMRC) about changes to their circumstances or income.
Customers whose circumstances have changed in the past year or who have received a letter to reconfirm their income details need to contact HMRC before the deadline of July 31.
Failing to respond by that date may mean people receive incorrect tax credits payments and may end up having to pay back any overpayments.
Tax credits help to top up the amount of money coming in for people on low incomes.
People are also being warned about scams, with criminals sending out messages purporting to be from HMRC, as the deadline approaches.
If someone texts, emails or calls claiming to be from HMRC, saying that a customer can renew a tax credits award or access financial help, and asks for credit card or bank details, it is likely to be a scam.
Information about recognising genuine HMRC contact is on the gov.uk website.
People can forward suspicious emails claiming to be from HMRC to email@example.com and texts to 60599.
If someone does think they have fallen victim to a scam, they should contact their bank immediately and report it to Action Fraud.
HMRC’s director-general for customer services, Angela MacDonald, said: “Tax credits provide much-needed financial support to our customers. But we know that many customers leave it to the last minute to renew their tax credits award.
“The time to renew your tax credits is now, you don’t need to wait until deadline day on July 31.”
Customers who received an annual review pack or text and have already made their declaration, including confirming their income and circumstances, do not need to do anything else, HMRC said.
However, customers need to contact HMRC straight away if they disagree with any of the information in the pack or letter or need to tell it about any changes.
In May, HMRC confirmed that people who cannot work their normal hours because of coronavirus would still receive their usual tax credits payments.
It said those working reduced hours due to coronavirus or who have been furloughed by their employer will not have their tax credits payments affected if they are still employed or self-employed.
These customers do not need to contact HMRC about this change and it will use the information it holds about the number of hours they normally work.
But people should tell HMRC if they or their partner lose their job, are made redundant or cease trading.
Customers can log on to gov.uk to check the progress of their renewal. They can also use the HMRC app on their smartphone to renew their tax credits, check their tax credits payments schedule and find out how much they have earned for the year.
Further information is available at www.gov.uk/manage-your-tax-credits.
Tax credits are gradually being replaced by Universal Credit.