WASHINGTON (AP) — More than 9 million people and families who did not receive their advance child tax credit checks, stimulus payments and other tax rebates will soon get a letter from the IRS to claim their money.

The tax credit was originally offered through President Joe Biden’s $1.9 trillion coronavirus relief package. The government says some families may be leaving up to $3,600 per child unclaimed, as well as other payments owed to them.

IRS Commissioner Chuck Rettig says many people who qualify for the tax benefits will need to file a 2021 federal income tax return to get the credit.

“We don’t want people to overlook these tax credits, and the letters will remind people of their potential eligibility and steps they can take,” Rettig said in a statement Thursday.

The letter, printed in English and Spanish, outlines eligibility requirements for the child tax credit, the earned income tax credit and others.

The child tax credit program, which was expanded during the pandemic, helped tens of millions of kids and their families, and contributed to a 46% decline in child poverty since 2020, according to a September report from the Census Bureau.

Since that program has ended, there are already indications that child poverty is increasing. Columbia University’s Center on Poverty and Social Policy estimates 3.7 million more children were living in poverty by January — a 41% increase from December, when families received their last check.

There are efforts in Congress to make the credit permanently available to all families with children.

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Associated Press writer Ashraf Khalil contributed to this report.