SIOUX FALLS, S.D. (AP) – The president of the union that represents workers at Smithfield Foods in Sioux Falls is urging them not to participate in a study of the effectiveness of an anti-malarial drug to treat the coronavirus.

Republican Gov. Kristi Noem said the state’s three largest health care providers will conduct a trial of the drug hydroxychloroquine pushed by President Donald Trump.

The Argus Leader reports United Food and Commercial Workers International Union president Marc Perrone said he was concerned by reports that patients treated with the drug had a higher death rate than those who received just standard care.

Sanford Health, which is conducting the trial, said there can be serious side effects from the drug, but they are rare.

Smithfield has closed the meatpacking plant indefinitely. About 800 workers at the pork processing plant and another 206 of their close contacts have tested positive for COVID-19 and two employees have died.

Noem’s spokeswoman, Maggie Seidel, said in an email that the hydroxychloroquine test is entirely voluntary.

“If folks want to go that route, the governor has done all she can to make it available,” she said. “It’s up to individuals and their doctors to assess whether it makes sense for them.”