Shares of the big credit-and-debit card payment networks rose after the United States Trade Representative accused the Chinese government of giving a local company called China Union Pay a monopoly over payment services in the fast-growing Chinese economy.

“China’s actions unfairly deprive U.S. credit and debit card companies of access to a huge market,” said U.S. trade representative Ron Kirk. He said “several hundred billion dollars worth of electronic payment transactions were processed in China in 2009,” and that under trade agreements the Chinese should have opened the market to global competition four years ago.

It’s not that the trade case is likely to deliver a sudden jolt to Mastercard and Visa’s bottom lines. The U.S. filing requests consultations — which the government described as just the first step in a case under the World Trade Organization.

It may be some time before we see any resolution: Parties that fail to resolve a dispute through consultations within 60 days may ask for a WTO dispute settlement panel to be seated, the U.S. said.

What’s more, there are other things going on in card land Wednesday. Mastercard issued a generally rosy outlook, which also surely contributed to the rally, and is buying back a lot of stock.

Still, U.S. financial firms are eager to get into the faster-growing parts of the world such as Asia and the Middle East, which hasn’t always been easy as a result of local support for national champions. Mastercard and Visa have both noted their plights in China in regulatory filings.

“In certain countries, our competitors have leading positions, such as China UnionPay in China, which is the sole domestic inter-bank bankcard processor and operates the sole domestic bankcard acceptance mark in China due to local regulation,” Visa said in its 10-K filing this year.

“Regulation can also play a role in determining competitive market advantages for competitors,” MasterCard said in its annual filing. “For example, China Union Pay is the sole domestic processor designated by the Chinese government and operates the sole national cross-bank bankcard information switch network in China due to local regulation.”

If nothing else, the trade case offers some hope that the companies will be able to push into the developing markets overseas sooner rather than later, helping to boost profits that might otherwise be pressured by the regulations passed here this year.

Mastercard rose 5.5% and Visa 2.6% in action Wednesday, though both remain far off their 52-week highs.