Some refined sugar imports from Mexico have been unfit for human consumption, according to the U.S. sugar industry.

Thanks to U.S. quality controls, the tainted sugar hasn't gotten into the food supply, the American Sugar Alliance said.

The shipments have caused food companies and candy manufacturers in the United States to rethink their long-held opposition to U.S. sugar policy, the group said.

When hurricanes ripped Louisiana's sugar cane fields last year, it resulted in a dramatic drop in U.S. sugar production.

Major users such as candy companies and food manufacturers couldn't get enough U.S. sugar to make their products. The U.S. Department of Agriculture responded to the shortage by increasing quotas on refined sugar from other countries.

The imports were supposed to arrive on the docks ready-to-eat, but many of the loads from Mexico contained fibers from the burlap sacks they were shipped in, ASA officials said.

Antiquated machinery in Mexico's processing plants also left behind metal grindings. And while hitching a ride in the shipments, rodents left behind their calling cards.

"When you see stuff come in with metal shavings and rat feces, it's not a product you can use," ASA spokesman Phillip Hayes said.

Consumers needn't worry. Thanks to U.S. quality controls, the tainted sugar was reprocessed at U.S. sugar refineries before being shipped to candy makers and food manufacturers.

Mexico's sugar refineries don't have the same standards as U.S. refineries, Hayes said.

"Our refiners have the highest quality standards in the world," he said.

The experience demonstrates the need for continued import controls, the U.S. sugar industry says.

American sugar policy allows refined sugar imports only rarely when U.S. supplies fall critically short of demand. Most imports come in the form of raw sugar that must be processed at U.S. refineries.

Besides import quotas, U.S. sugar policy provides for "non-recourse," government loans to processors. If sugar prices fall below an established floor price, processors have the option to forfeit sugar supplies to the government in lieu of loan repayment.

Major sugar users have repeatedly called on Congress to scrap the policy, but the tainted imports from Mexico have caused them to quietly change their tune, ASA officials said.

It has been a "monumental shift" in attitude for candy companies and food manufacturers, Hayes said.

"This was really a wakeup call," he said. "They have really shifted their tone on Capitol Hill."

In the past, end-users have suggested that America could simply import all of its refined sugar needs from other countries.

"They certainly aren't thinking that way anymore," Hayes said.

"Their rhetoric isn't quite as sharp anymore, and we believe it's because of the quality issue with these imports," he said.

Major end-users and sugar producers still don't see entirely eye to eye.

The Sweetener Users Association in August unveiled a plan to replace the existing U.S. sugar program with a $1.3 billion-per-year plan based on direct government payments to producers.

The plan has received only a lukewarm reception on Capitol Hill.

The U.S. sugar industry is strongly opposed to the direct subsidy plan and wants to retain existing policy, Hayes said.