SYDNEY » When Steve Franklin bought four plane tickets on Qantas last June, he faced an unexpected expense: a surcharge of 7.70 Australian dollars on each of the 136.70-dollar ($126) tickets—just for using his Visa credit card.

Franklin, who planned to fly his parents and his 7-year-old twin daughters from Sydney to Adelaide, knew that changes to credit card rules had affected the cost of using plastic, but the extra 5.6 percent seemed excessive.

The charges were the consequence of changes in credit card rules in Australia that were aimed, in part, at reducing the cost of hidden fees for using plastic. But the law, passed six years ago, also allowed merchants to tack on new charges, and many have done just that, in some cases with fees that exceed the old ones.

Now, as Congress debates how to rein in credit and debit card companies in the United States, Australia's experience is being pointed to as an example of just how tricky that can be: For one thing, if regulators limit one fee or rate, banks are likely to find another way to keep revenue flowing.

As in Australia, the stakes are high in the United States. American merchants, like their counterparts Down Under, complain that the high fees they must pay credit card companies and banks to accept their cards force them to increase prices on everything they sell—even for people who pay with cash—to make up the difference.

In the United States, the Government Accountability Office last week issued a report showing that consumers who did not use credit cards “;may be made worse off by paying higher prices for goods and services, as merchants pass on their increasing card acceptance costs to their customers.”;

The main consumer federation in Australia, Choice, says that while regulations here have had a few unintended consequences, they have created incentives for retailers and consumers alike to rely more on debit cards, which have much lower processing costs, instead of credit cards. “;It drives me crazy, people buying chewing gum on a credit card,”; said Christopher Zinn, a spokesman for Choice, an Australian consumer group. “;We all pay for it.”;

Though many people may not realize it, out of every dollar charged on a credit card, merchants in many countries, including the United States, get about 98 cents and sometimes less; the other 2 cents go to banks and credit card companies. Banks use these fees to cover fraud losses, their loss of interest on money until the consumer pays the bill, computer systems and employees who process credit card transactions. The banks also pay Visa and MasterCard for their marketing and digital networks.

But the fees also generate tens of billions of dollars in revenue each year for banks that issue cards branded by Visa and MasterCard. In the United States alone, banks that issue credit cards get an estimated $40 billion to $50 billion in income annually from interchange fees, which are the biggest single component of fees charged to merchants. The banks and card companies are lobbying heavily against proposed changes. They warn that lower fees will lead them to squeeze credit and raise the cost of credit cards at a time when the economy thirsts for credit to sustain an economic recovery.

Some of this has already happened in Australia, where in 2003, after years of retailers' complaints, the nation's central bank required that the interchange fees that merchants pay banks that issue Visa and MasterCard cards be cut in half, to less than 1 cent. Merchant fees for American Express and Diners' Club were not regulated because banks did not issue their cards. But both card companies cut merchant fees anyway, to 2 cents, from 2.46 cents, to avoid losing customers to Visa and MasterCard.

That difference may sound tiny—what's a penny?—but banks and card companies say the lower fees have cost them about 1 billion Australian dollars annually, or $919 million. And they have turned to Australian consumers to make up the revenue.

Since the government policies went into effect, Australian banks have cut credit card perks and shrunk rewards programs, like frequent-flier miles. While it used to take 12,400 Australian dollars of spending on Visa or MasterCard from one of the country's four biggest banks to earn a 100 dollar shopping voucher, for instance, now it takes 17,000 dollars.

Banks now also require customers to pay their bills faster. Interest starts accumulating on many cards 33 or 44 days after the start of a billing period, instead of the previous 55 days.

Annual fees have also climbed for credit cards with reward programs, to 140 Australian dollars a year for gold cards that carry rewards, up from 98 dollars before regulation of interchange fees. Basic cards without rewards still carry on average an annual fee of 29 Australian dollars.

Perhaps more vexing, Australian merchants, including retailers, restaurants and airlines, are imposing surcharges for each credit card transaction, even though fees the merchants pay card companies have fallen.

“;I feel like Qantas was trying to nickel-and-dime me,”; Franklin said. Qantas said that it was merely trying to recoup the fees it still had to pay to banks and card companies, a cost it does not incur when a customer pays cash or uses a debit card.

Indeed, after the Australian central bank allowed companies to start levying surcharges, many began to impose large and rising ones on credit card use. Some companies have even figured out a way to make a profit. For instance, Accor, a global hotel giant with 11 brands ranging from the luxurious Sofitel chain to Motel 6, introduced a 1.5 percent fee here last February for credit card users.

“;It has aided our profit margins,”; said Michael Issenberg, Accor's chairman of the Asia and Pacific region, who added that the hotel chain had seen little consumer resistance.

Consumer advocacy groups see such profits as an unintended consequence for consumers of the central bank's changes. Choice, an Australian consumer group, has joined with Visa and MasterCard to ask the government to restrict retailers from making gains from the surcharges. No one is suggesting outright surcharges for paying with a credit card in the United States, although one congressional bill would make it easier for merchants to charge consumers less if they pay with debit cards or cash, something card companies oppose.

Visa, MasterCard and the banks that issue their cards prohibit retailers from charging extra if consumers pay with credit instead of cash, out of fear that more people would use cash if they knew that using plastic would cost more. Where exceptions are allowed, as in some gas stations, retailers must list the cash and credit card prices for each item. In Australia, the central bank overrode the banks, and card companies' rules, to authorize surcharges.

In addition, other bills in the House and Senate would allow merchants to band together to negotiate lower fees with Visa, MasterCard and others; now, retailers have little choice but to accept the terms they are offered or not accept credit cards, which could result in losing customers.

But banks in the United States warn that, as in Australia, American consumers may see the costs of using a credit card rise, and the benefits decline, if Congress passes legislation to reduce interchange fees. While American retailers had once pushed for changes unsuccessfully, there is new momentum this year after Congress passed credit card reforms in the spring aimed at curbing excessive fees and interest on credit cards.

Among retailers, 7-Eleven is leading a push to persuade Congress to adopt the “;Australia option”; and is calling on the Federal Reserve to cap and closely regulate merchants' credit card fees. In September, 7-Eleven sent more than one and a half million signatures to Washington from customers who, the chain said, believed Congress should limit merchant fees because they tended to raise the price of goods.

“;There's certainly an awareness on Capitol Hill of Australia, and a lot of interest,”; said Keith Jones, the government relations director for the Southland Corp., which runs the 7-Eleven chain.