Uncle Sam is worried that some people aren't getting their Earned Income Tax Credit, worth up to $5,751 for the 2011 tax season.

The tax credit is to help low- or moderate-income workers with those having children getting more of a credit. Those eligible for the credit can get a refund even if they owe no tax.

But the IRS estimates that one out of five eligible tax filers fail to claim it. People may not be aware of it since they have not previously been able to qualify for it, according to the Internal Revenue Service..

"Many people who have experienced changes like going from full-time to part-time work, had their salary reduced or had a baby may not know that they qualify for the credit for the first time," the IRS said.

Most low to moderate-income parents are savvy about the tax credit that, in most cases, puts thousands of dollars in their pocket each year, said Mark Daily, owner of seven Jackson Hewitt franchises in South Florida.

They tend to file early because they need the refund. "They use it to get a new apartment or buy a used car," he said. "It's a boost to the economy."

The people who may not know they qualify are the single filers, Daily said. But the credit for singles is only a fraction of what parents get.

For the 2011 tax year, Jackson Hewitt says the maximum credit is:

$5,751 for three or more qualifying children

$5,112 for two qualifying children

$3,094 with one qualifying child

$ 464 with no qualifying children.

To qualify for the tax credit, workers must have total earned income and adjusted gross income less than:

$43,998 (or $49,078 for married filing jointly) with three or more qualifying children.

$40,964 (or $46,044 for married filing jointly) with two qualifying children.

$36,052 (or $41,132 for married filing jointly) with one qualifying child.

$13,660 (or $18,740 married filing jointly) with no qualifying children.