The next time you go to use your credit card better hope you haven't exceeded the limit. The tough economy is hitting credit card companies too, and many customers are discovering they no longer have credit.

When Mary Horowitz tried to treat herself to a day at the spa for her 28th birthday, she got a big surprise.

"The girl at the counter told me my card was declined," she recalls.

Horowitz was shocked. She had a zero balance, and had carried American Express for 5 years. So she called to find out what was going on.

"They told me that my card had actually been canceled the previous week because of delinquent history on my credit report. I asked specifically, what late payments, what delinquencies? They couldn't give me an answer," Horowitz says.

Millions of Americans have had the same experience. John Ulzheimer is an economist. He says this is not unusual.

"Many credit card issuers are proactively cleaning house--a consumer who either doesn't use the card, or under-utilizes the card, is simply not generating revenue for the credit card issuer," Ulzheimer explains.

With such a large number of people out of work, banks are scrambling to reduce their exposure to potentially bad credit lines.

"Everybody presents a higher risk than they did a year ago, and each individual card company is going to look at their own portfolio, their own customers," Ulzheimer says.

According to one Wall Street analyst, half of all credit lines available in the U.S. may be rescinded by the end of next year. While you'll get a warning if your interest rate is about to go up, you may not know if your credit limit has been slashed, or if you're about to lose the credit altogether.

As for Horowitz, she got a new credit card, but she's reluctant to use it. "We decided to go to a cash only system. If we don't have the money, we don't buy it."

The good news is you now have longer to pay your bill. The new credit card laws that just went into effect require companies to send you the statement a full three weeks before it's due. The new law also requires companies to give you 45 days notice before changing your interest rate or your rewards program.