HONG KONG — An unusually broad coalition of business groups in North America, Europe and Asia has sent a letter to the heads of state of the Group of 20 major economies, asking them to make a commitment at their meeting this month in Seoul that trade in crucial rare earths will not be interrupted because of industrial policies or political disputes.

The range of countries and industries whose business groups signed the letter underscores the level of worry in corporations around the world about recent export restrictions placed on rare earths by China, which mines 95 percent of such materials. The minerals processed from them are needed for products and processes like cellphones, cars, clean energy and the production of missiles and sonar.

Some of the business groups signing the letter, like the U.S. Chamber of Commerce, also signed a letter last winter asking that the Chinese government not discriminate in favor of domestic companies in the purchase of high-technology equipment.

But the letter on rare earths was also signed by business groups that had previously been wary of challenging an increasingly wealthy China, including the business federations of Germany and France and the Nippon Keidanren, the broad grouping of big Japanese corporations that has historically been extremely cautious on China issues.