BEIJING -- Two U.S. senators, part of a delegation to China this week, are pressing Chinese officials to ease protections on its currency before the Senate votes on possible punitive measures next week.

Sen. Lindsey Graham (R-SC) and Sen. Charles Schumer (D-NY) claim that China is manipulating its currency, in violation of World Trade Organization rules.

The U.S. Senate has set a March 31 deadline to vote on a bill to impose tariffs of 27.5% on Chinese imports. The bill, proposed by Graham and Schumer, is a response to China's enormous trade surplus with the U.S., a sum that the legislators say is exacerbated by China's refusal to float its currency on the world markets.

Last year, China had a trade surplus of $202 billion with the U.S.

Many legislators and analysts claim the yuan, if floated, would rise sharply in value, thus increasing the cost of Chinese goods on foreign markets.

China has resisted such measures, in part for fear of an inflation spike that would hurt its residents. Under pressure last year, the nation agreed to price the yuan within a narrow band of foreign currencies, with controls in place for how much its value could change during a given period of time. Those controls have effectively kept the yuan in line with the dollar.

But the senators weren't backing down in Beijing. "The currency issue is the defining moment for U.S.-China relations," Graham was quoted as saying. "There's a backlash growing in our country — right or wrong — from the idea that the Chinese do not follow normal business practices.

"They're too large and they're too influential not to be asked to abide by normal business rules of the international business community."