The extraordinary unity the world's major economies mustered to fight the financial crisis is in jeopardy of coming undone over no-name tires and chicken feet.

With less than a fortnight to go before hosting a summit of the Group of 20 nations in Pittsburgh, U.S. President Barack Obama Monday was defending his decision to implement punitive duties on $1.8-billion (U.S.) of lower-end Chinese tires at the behest of the United Steelworkers union.

Unlike some trade complaints, the 35-per cent-levy was Mr. Obama's decision alone, making it an overtly political move rather than an administrative one.

The Chinese government's response was layered with insult, causing trade lawyers and former government officials to fret about the possibility of a trade war.

Beijing called the White House's decision an “abuse” of U.S. trade law, filed a complaint at the World Trade Organization and initiated an analysis that could result in tariffs on about $2-billion of U.S. chicken products and automotive parts.

Mr. Obama denied his decision was “protectionist,” a dirty word when it comes to talking about the financial crisis because leaders have been so vigorous in their claim that they have learned the lessons of the Great Depression, which was exacerbated by restrictive trade policies.

U.S. officials were firm in repeating that last week's decision to place duties on Chinese tires was entirely consistent with provisions that allow the president to seek to correct “surges” in imports that undermine domestic production. The risk is that the international consensus forged to fight the financial crisis isn't strong enough to withstand a blow that could be interpreted as a show of bad faith by the U.S. president.

The U.S. and Canadian governments already are set to clash with European leaders such as French President Nicolas Sarkozy over regulating bankers' compensation. Unity is important because joint government stimulus is effectively the only reason the global economy is showing signs of coming back to life.

“This has added a heck of a lot more tension to a system that didn't need it,” said Clay Lowery, managing director at Washington-based Glover Park Group and a former official in the international affairs branch of the U.S. Treasury Department. “One of the concerns about the G20 is that it's all about rhetoric – and here is the U.S. government demonstrating that that's the case.”

When the G20 leaders met for the first time ever in Washington in November, they pledged to “refrain” for a year from policies that would impede trade, and extended the promise to the end of 2010 at their second gathering in London in April. For the most part, governments have made good on that commitment, said Pierre Pettigrew, an adviser in the Toronto office of consultancy Deloitte and a former Canadian trade minister.

A joint report by the WTO, the Organization for Economic Co-operation and Development and the United Nations made a similar conclusion yesterday. Still, those agencies said there has been “policy slippage” since the April meeting, and their report called for “particular restraint” in the use of measures like the one Mr. Obama used to target Chinese tires.

Trade lawyers and other analysts were reluctant to declare a Sino-American trade war.

However, Brenda Swick, an Ottawa-based trade lawyer at McCarthy Tétrault LLP, noted Mr. Obama's unusual decision to heed a trade complaint registered by a union opens the door to similar grievances. John Curtis, a former chief economist at the department of international trade, said there's a lot riding on how China chooses to respond. “This might trigger what we all have been dreading,” said Mr. Curtis, who is now a distinguished fellow at the Waterloo, Ont.-based Centre for International Governance Innovation. “This could spiral out of control.”

With files from Bloomberg News and Reuters