The Food and Drug Administration must halt all primate experimentation at an Arkansas laboratory until allegations of negligence and abuse are properly addressed, U.S. congressmen demanded in a bipartisan call for action.

U.S. Reps. Matt Gaetz, of Florida, and Brendan Boyle, of Pennsylvania, submitted a letter to FDA Commissioner Scott Gottlieb March 21 after they learned of the Aug. 3 death of a 5-year-old rhesus monkey at the National Center for Toxicological Research near Pine Bluff, the Associated Press reported Wednesday.

"Enough is enough," Gaetz, a Republican, said Tuesday. "Taxpayers are sick and tired of the government's multimillion-dollar monkey business, and I'm proud to lead bipartisan efforts to cut wasteful and abusive primate research at the FDA."

A nicotine-addiction study at the lab started in 2014 with 24 male squirrel monkeys — 12 adults and 12 adolescents — but Gottlieb permanently terminated that study in January 2018 after four of the animals died. The surviving primates from that study were retired to a sanctuary in Florida.

But monkeys are still being used in other tests at the Jefferson County facility.

Gaetz and Boyle, a Democrat, wrote to Gottlieb on Oct. 26 "applauding" his decision to halt nicotine testing on primates at the lab.

But in their March letter, they said the death in August of a monkey involved in another test suggested "a persistent lack of proper oversight, animal care and training" at the center. The director of the center said the animal was accidentally strangled when it was left in a restraint chair in a test chamber.

Gottlieb did not return a request for comment on Tuesday. The Washington Post reported that Gottlieb has resigned effective next month. Norman "Ned" Sharpless will serve as interim commissioner.

Advocates for ending animal testing urged the lawmakers to keep up the pressure on the agency.

"Over 1 million of our supporters have asked Congress and the FDA to stop wasteful primate testing and retire the animals to sanctuaries, and we're grateful to Reps. Boyle and Gaetz for continuing to hold the FDA accountable for its taxpayer-funded animal abuse," said Justin Goodman, vice president of advocacy and public policy at the White Coat Waste Project, an alliance that aims to stop government spending on animal experiments.

Renowned wildlife expert Jane Goodall wrote to the FDA in September 2017, calling the study “cruel and unnecessary.”

“To continue performing nicotine experiments on monkeys when the results of smoking are well-known in humans — whose smoking habits can be studied directly — is shameful,” she wrote.

Most research primates worldwide are macaques or marmosets. They are used in relatively small numbers (they make up around 0.1 percent of research animals, but they have been important in many important medical advances; for example the polio vaccine, life support systems for premature babies, and deep brain stimulation for Parkinson’s Disease, according to the British Research firm Understanding Animal Research.

Currently the main areas of primate study are infectious diseases to develop vaccines and treatments for HIV/AIDS and malaria; in neuroscience to better understand the brain and treat conditions ranging from Alzheimer’s disease to schizophrenia; and in reproduction, fertility and fetal research. They are also used in safety testing new medicines and vaccines.