Penny-pinching Citibank will put the squeeze on small-fry customers, charging them up to $90 a year by demanding a fee every time their average monthly checking account balance sinks below $1,500.

Starting in February, Citibank will no longer automatically waive its $7.50 monthly fee for its “EZ” and “Access” checking-account holders who make either a direct deposit, or two bill payments online monthly.

“Yes, we’re changing certain terms and conditions for our EZ and Access checking-account packages,” a spokeswoman said.

“Regarding what prompted us to make these changes, we did so to make them more simple and straightforward, by recognizing and rewarding customers for maintaining their balances with Citibank.”

But one Citi manager admitted the extra fees will be a tough sell, and likely will send many of his less-well-off customers to rival banks.

“Some are regular working folk who are trying hard to make ends meet and to pay their bills,” said the manager. “Fifteen hundred dollars is a lot of money. Many don’t have that kind of balance in their accounts.”

Fees are lucrative to banks. Pulling an extra $90 a year from its customers’ pockets may not seem like a lot of money to a bank, but multiply it by thousands of accounts and the dollars quickly add up.

“When this is aggregated, it can be highly significant,” said James McNulty, a finance professor at Florida Atlantic University in Boca Raton.

And if Citi finds that customers don’t flee, other banks might be tempted to copy it, said Peter Cohan, a management consultant. “If it turns out that this bank makes a lot more money from the move, other banks will start to do the same.”

But some of the more “customer-oriented” of the nation’s 8,500 banks may be tempted to attract new business simply by advertising the fact they do not charge maintenance fees, Cohan said.

He also warned that the Obama White House would not look too kindly on banks “trying to squeeze pennies out of the poor.”

With the rise of “free checking” offers, most bank customers pay very little in bank fees. About 70 percent of consumers spend $3 or less in monthly fees for checking account maintenance and ATM access, the American Bankers Association says.

And 56 percent pay nothing. That’s up from 52 percent in 2008, the ABA’s survey found.

Citibank’s move to boost fees comes as two of its main rivals, Bank of America and Chase, are taking an opposite tack, by curbing charges for overdrawn accounts.

Bank of America recently announced it would simply stop imposing fees on customers who overdraw their accounts by less than $10. It’s also limiting the number of fees for individual overdrafts to four per day.

Chase is eliminating overdraft fees on debit cards unless customers opt in. Customers who agree to the fees will be allowed to overdraw their accounts; those who do not agree to the fees will be declined if they try to overdraw their accounts.

Chase will also stop charging fees when accounts are overdrawn by less than $5.

The changes come as Washington lawmakers push proposals to eliminate what critics say are unfair bank charges and fees.