The Trump administration has warned more than 1,100 Environmental Protection Agency employees who work on climate change, reducing air pollution, enforcing environmental laws and other programs that they could be fired at any time.

An email, reviewed by The New York Times, was sent to staff members who were hired within the past year and have probationary status. Many of those employees were encouraged to join the E.P.A. under the Biden administration to rebuild the agency, which had been depleted during President Trump’s first term. Others are experienced federal workers who had taken new assignments within the agency.

Many had been hired to work on programs that Congress created through two recent laws, doing things like helping communities replace lead pipes, mediating toxic sites and funding clean energy projects aimed at reducing the greenhouse gas emissions that are heating the planet.

“As a probationary/trial period employee, the agency has the right to immediately terminate you,” the email states.

Molly Vaseliou, an E.P.A. spokeswoman, said in a statement that “our goal is to be transparent.” She declined to answer questions about the email, though, including whether Lee Zeldin, the agency’s new administrator, intended to terminate employees and, if so, for what reason.

“On his first day in office, he engaged directly with career staff across E.P.A.’s headquarters — spanning two city blocks in downtown D.C. — listening to their insights and perspectives,” Ms. Vaseliou said. “Ultimately, the goal is to create a more effective and efficient federal government that serves all Americans.”