NEW YORK (CNNMoney.com) -- Get ready for a smaller paycheck.

At least that's what could happen if Congress doesn't approve President Obama's proposal to extend the Making Work Pay tax credit soon.

The credit, introduced last year as part of the government's stimulus package, boosts paychecks by up to $400 for single filers and up to $800 for joint filers, by reducing the amount of tax withheld from each paycheck.

And that extra $15 bump you're used to getting each bi-weekly pay period is slated to expire at the end of the year unless Congress votes to extend the credit, much like the Bush tax cuts.

But unlike those cuts, which were largely viewed as a benefit for wealthier Americans, the Making Work Pay credit is designed exclusively as a middle-class benefit,...