Congress and federal regulators may be clamping down on overdraft fees, but consumers may be seeing what some critics say is an even sneakier type of charge increasingly showing up on bank statements: the monthly maintenance fee.

Checking account maintenance fees had been a rarity in the past several years as banks threw offers of free checking at consumers in hopes of attracting deposits. Now, free checking itself may be headed toward extinction as both the size of monthly fees and the number of banks that charge them are on the rise.

Account maintenance fees increased by 15% between the first and third quarter of 2009, according to Money-Rates.com, a site that compiles data on banking products interest rates. (During the same period, overdraft fees increased by 2.8%.) While 44% of checking accounts surveyed had no maintenance fees in the first quarter of 2009, that number was down to 37% in the third quarter.

For depositors, the trend is troubling. Unlike overdraft fees, these account maintenance fees can affect even the most financially responsible consumers, says Richard Barrington, a banking analyst at Money-Rates.com.

With the average account maintenance fee now at $6.63 per month, a consumer whose checking account balance averages $500 will pay nearly 16% each year -- a rate that consumers are likely to associate more with their credit cards, not their checking accounts.

You can control overdraft and ATM fees by modifying your behavior, but monthly fees are there, month after month, no matter what you do, Barrington says.

Citibank is one example of a large bank where more customers could soon wind up paying fees. The bank recently informed its EZ and Access checking account holders that, starting in February, it will no longer waive the accounts $7.50 monthly fee for those who have set up direct deposit or make at least two online bill payments a month. To avoid the fees, customers will have to maintain an average minimum balance of $1,500.

Citi is one of the first big banks to tighten the strings around its free checking product, but it s likely not the last. The large banks were offering free checking largely because it was being subsidized by overdraft revenue, says Greg McBride, a senior financial analyst at Bankrate.com. If overdraft revenue goes away, the large banks don t need to offer free checking as a way to bring in deposits. They already have more deposits than they know what to do with.

Citi spokeswoman Natalie Riper says the bank s decision to remove the direct-deposit waiver has nothing to do with the Fed s overdraft rules. Riper says Citi doesn t allow overdrafts on debit-card purchases or at ATMs to begin with, so the new rules don t affect the bank.

Riper says the goal behind Citi s move is to encourage its customers to do more business with the bank. The $1,500 minimum balance requirement, for example, is a combined requirement for all accounts held by an individual. So customers could avoiding the fee by opening a savings or money-market account, or putting their money in a certificate of deposit.

Because they encourage customers to stay with a bank longer, features like direct deposit and online bill payments have been common requirements for free checking accounts. Providing free checking is a loss leader, McBride says. Getting the hooks on the consumer increases the likelihood that they ll stick around long enough to become profitable. With less profit-making potential at least when it comes to bringing in overdraft fees most large banks are likely to introduce minimum balance requirements and monthly fees to their lineups, McBride says.

The good news for consumers: There are options. Here are three ways to avoid monthly maintenance fees:

1. Shop around

Community banks, credit unions and online banks have typically offered free checking and will probably continue to do so in the future, McBride says. Banks play on the fact that people don t switch checking accounts too often. Outsmart your bank by finding a free checking account elsewhere.

2. Pool your resources

If your bank introduces a minimum balance requirement, chances are that will include a range of product offerings, Barrington says. If moving part of your rainy-day fund into a savings or money-market account at the same bank will help you meet that minimum, it s a step worth considering.

3. Take advantage of special offers

Many banks have special offers for certain demographics. Free checking is still widely available for students and retirees, Barrington says. Check with your employer, as well: Many companies have bank at work programs, which waive account fees for employees at a certain institution.

Here s a look at some checking-account programs at a variety of banks, including their maintenance fees: