Under heavy pressure from unions to rule as it did, the administration made its decision following a Labor Department assessment that public sector work, from cleaning streets to processing government forms, qualified as work under the Fair Labor Standards Act.

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Some have only shown traces, which may be the result of meat processing plants not properly cleaning equipment.

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She said trace contamination with other animals - including pig and horse - could take place at abattoirs and processing plants dealing with more than one species "even with thorough cleaning and good hygiene practice".

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Diversey, No. 121 on the 2010 list of largest U.S. companies, makes commercial cleaning compounds and equipment and its offerings include commercial floor wax, sanitizers for restaurants and food-processing companies, cleansers and deodorizers for restrooms, and industrial degreasers.

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