The Environmental Protection Agency has placed roughly 140 employees on administrative leave days after they signed a public letter expressing concern about the treatment of federal employees and the Trump administration’s regulations on climate and public health.

Environmental Protection Agency staffers who signed a letter criticizing Trump administration policies were placed on leave Thursday. The EPA said it placed 144 staffers on administrative leave as it investigates the letter.

Two employees in the EPA’s Region 8 headquarters in Denver and one who works at the EPA’s National Enforcement Investigations Center in Lakewood are under investigation for signing the letter, said Kate Tribbett, vice president of the American Federation of Government Employees Local 3607, which represents Region 8 employees.