One mistake could cost Trina Lee her Christmas.

Things have been tight for the Arizona-based nursing assistant since she got laid off two years ago and suffered some medical problems that have kept her from working full-time.

As a result, she's become meticulous about watching her bank balance, which is often uncomfortably close to zero.

Earlier this month, she was feeling temporarily flush because she had prepaid most of her bills and figured out that the rest of her December income from child support and a part-time job could be spent on Christmas gifts.

So she splurged on a $65 meal with her mom and brother, knowing it was possible that this one meal could overdraft her checking account.

Debit-card transactions like this one require a signature and usually take a couple of days to clear, so Lee monitored every purchase after that, copying her daily bank-account activity into a computer file each night to make sure she wasn't stepping over the line.

On Dec. 7, the night before her son's child-support payment was due, she breathed a sigh of relief. At 10:45 p.m., the dinner charge still hadn't posted and wasn't even listed as pending.

After subtracting every pending payment, she had precisely 16 cents in her checking account. She went to bed imagining that she'd dodged an overdraft because she would get a $156 payment in the morning.

She got a rude awakening.

Before crediting her account for the child-support payment, Chase bank not only put through the dinner charge, it also "reordered" every one of her pending transactions, turning one potential overdraft into four.

The mounting overdraft charges of $35 each then triggered two additional overdraft charges for small debit transactions that Lee did that day, before she'd realized that her account had gone into the red.

In total, Chase levied $210 in overdraft charges -- $175 more than Lee imagined was possible.

"I accept responsibility for one overdraft," said Lee, a 29-year-old mother of two. "But they created the rest of these. It's really frustrating."

Bank spokesman Greg Hassell said Chase would not reverse these charges because "Ms. Lee intentionally overdrafted her account, knowing she had insufficient funds for all her purchases."

The fact that Chase in effect created five of the six overdrafts by changing the order of her transactions -- deducting the biggest items first to drain her account faster -- is simply current policy, the spokesman said.

The policy is common among big banks, industry experts say.