North America's largest union for hotel, restaurant and kitchen workers has called on manufacturers of cooking oils to stop using diacetyl, a lung-destroying butter-flavoring additive, and members of Congress have called for a federal investigation into the use of diacetyl, including where and how it's being used and whether workers are being harmed, the Seattle Post-Intelligencer reports.

"It could pose a serious health risk to commercial cooks and UNITE HERE is calling for fast action by the food industry to cease the use of diacetyl flavoring in commercial and home cooking products," the union representing 450,000 workers said in a written statement.

The union was reacting to recent results of laboratory analysis of 23 cooking oils, sprays and margarines used by both home and professional cooks. The analysis, conducted by the certified laboratory LabCor, found diacetyl vapors were released in all the products when the manufacturer's recommended amount of margarine, oil or spray for a specific recipe was heated.

The highest levels of diacetyl were found in the testing of butter-flavored pan, grill and sauté oils used by professional cooks. An extrapolation of the toxic vapors released over a typical four- to five-hour breakfast rush matched or exceeded the diacetyl levels found in some microwave popcorn plants where hundreds of workers have been sickened. The deaths of at least three from bronchiolitis obliterans — inflammation of the small airways in the lungs — were attributed to exposure to the chemical butter flavoring.