The Environmental Protection Agency (EPA) is placing staffers who signed a letter of dissent against the Trump administration’s actions and policies on leave.

The EPA says it has placed 144 staffers on administrative leave as it investigates the letter. It’s not entirely clear whether they will face further punishment after the probe.

“The Environmental Protection Agency has a zero-tolerance policy for career bureaucrats unlawfully undermining, sabotaging, and undercutting the administration’s agenda as voted for by the great people of this country last November,” EPA spokesperson Brigit Hirsch said in a written statement. 

In a letter made public on Monday, current and former EPA staffers said that the administration’s policies “undermine the EPA mission of protecting human health and the environment.”

They expressed concerns about five issues in particular, saying that the administration is undermining public trust, ignoring scientific consensus to benefit polluters, reversing EPA’s progress in America’s most vulnerable communities, dismantling the Office of Research and Development and promoting a culture of fear.

“Your decisions and actions will reverberate for generations to come. EPA under your leadership will not protect communities from hazardous chemicals and unsafe drinking water, but instead will increase risks to public health and safety,” the staffers wrote to Administrator Lee Zeldin.

In response, the EPA said Monday that it would “continue to work with states, tribes, and communities to advance the agency’s core mission of protecting human health and the environment.”

Nicole Cantello, president of the American Federation of Government Employees (AFGE) Local 704, which represents EPA employees in the Midwest, told The Hill that putting staffers on administrative leave was ” blatant retaliation by the Trump administration.”

“We don’t swear an oath to the Trump administration, we swear an oath to the Constitution  and so we don’t feel  like we violated that oath or that we did anything wrong by signing this letter,” she said, adding that some of the staffers who were placed on leave are actually “crucial players in trying to implement Trump’s policies at EPA.”

Zeldin told reporters in January that staff who are “not committed” to President Trump’s directives should not be there. 

“I don’t believe that anyone should be here at EPA who is not committed to the agency mission and the lawful directives coming from the duly elected president of the United States,” he said at the time.

The EPA previously fired staff who worked on issues related to environmental justice and tackling pollution in underserved communities, arguing that it did not align with the administration’s position on diversity, equity and inclusion.

Updated at 1:19 p.m. EDT