Employees of the Environmental Protection Agency have been calling their senators to urge them to vote on Friday against the confirmation of Scott Pruitt, President Donald Trump’s contentious nominee to run the agency, a remarkable display of activism and defiance that presages turbulent times ahead for the EPA.

Many of the scientists, environmental lawyers and policy experts who work in EPA offices around the country say the calls are a last resort for workers who fear a nominee selected to run an agency he has made a career out of fighting — by a president who has vowed to “get rid of” it.

“Mr. Pruitt’s background speaks for itself, and it comes on top of what the president wants to do to EPA,” said John O’Grady, a biochemist at the agency since the first Bush administration and president of the union representing the EPA’s 15,000 employees nationwide.

Nicole Cantello, an EPA lawyer who heads the union in the Chicago area, said: “It seems like Trump and Pruitt want a complete reversal of what EPA has done. I don’t know if there’s any other agency that’s been so reviled. So it’s in our interests to do this.”