Your first 2013 paycheck: A change you need to know about the change in payroll tax

(CBS News) -- The first paycheck of this year contained a surprise for many workers. Their take-home pay has dropped by at least two percent.

That means if you make around $50,000 you will take home $18 to $20 a week less, and double that amount if you make $100,000 or more.

"It doesn't seem like a lot, but that money, it's important, it really does matter," Jill Schlesinger, editor-at-large for CBS Moneywatch, said on "CBS This Morning."

"It could be the difference between you making enough money, $1,000 over the course of the year, to really pay your bills," she said. "It also could be the amount that you needed to put into your retirement account. It could be the amount you needed to pay down your credit card debt. This is a very important number for families, especially those living on the edge. I got to remind everyone, you're one of the 160 million people who work, your taxes have gone up this year."

It's happening because Congress and the president allowed a temporary cut in Social Security withholding to expire. But what does that mean?

Schelsinger explained, "Employees, we pay 6.2 percent, your employer pays 6.2 percent, as well. A couple years of years ago when the economy was really fragile, one of the ways to stimulate the economy was to lower the payroll tax for employees, so it went from 6.2 percent of your earnings, down to 4.2 percent. That was awesome. It helped you get a little bit more money in your paycheck. Unfortunately, sadly, now we're back at 6.2 percent. It was not extended as part of the 'fiscal cliff' negotiations."

However, some economists critical of the move are saying it may affect consumer spending. Schlesinger said, "A lot of the economists I talk to all the time were up in arms about this because they think that this payroll tax cut was a great form of stimulus. And now the resumption of that 6.2 percent number means we're probably going shave about a half a percent off our growth rate this year. You think, 'Oh, a half a percent, not a big deal.' We're only growing by two percent a year so it is a big deal."