A group representing the U.S. cement industry says a federal government plan for cutting emissions of mercury and other air toxins at its plants is unrealistic.

The Portland Cement Association said Wednesday a regulation drafted by the Environmental Protection Agency would cause some plants to close. The group said there would be shortages of cement, the key ingredient in concrete.

The industry also predicted more cement imports from countries with weaker standards.

EPA’s proposed rule would require the nation’s 99 cement plants to make steep reductions in releases of pollutants such as mercury, hydrochloric acid, hydrocarbons and soot.

The agency says cement kilns are America’s fourth-largest source of airborne mercury. It says the proposed limits would save up to 1,600 lives a year.