More than 1,000 current and former federal health workers demanded the resignation of Secretary of Health and Human Services Robert F. Kennedy Jr. in a letter on Wednesday, a week after he facilitated the ouster of former Centers for Disease Control and Prevention Director Susan Monarez.

Kennedy has increasingly faced scrutiny from within HHS, partly because of his long-held vaccine skepticism, which the workers argued has influenced his decision-making. Monarez’s firing and the resignations of four CDC officials only accelerated the staff revolt against Kennedy.