More than 1,000 employees of the Centers for Disease Control and Prevention have signed a letter calling for the agency to address “a pervasive and toxic culture of racial aggressions, bullying and marginalization” against Black employees.

The letter, a copy of which was obtained by The New York Times, was first reported by National Public Radio on Monday. It was sent to Dr. Robert R. Redfield, the director of the C.D.C., on June 30.

“After decades of well-meaning, yet underfunded, diversity and inclusion efforts, we have seen scant progress in addressing the very real challenges Black employees experience at C.D.C.,” the letter said, pointing to a “lack of inclusion in the agency’s senior ranks” and “ongoing and recurring acts of racism and discrimination.”

The letter comes as the C.D.C. is confronting the most urgent public health emergency in its 74-year history. The federal response to the coronavirus pandemic has been characterized as slow and ineffectual, and some have criticized the C.D.C. for its failure to anticipate and explain the pandemic’s effect on Black and Latino people.

At the same time, widespread demonstrations for racial justice following the killings of George Floyd, Breonna Taylor, Tony McDade and others at the hands of the police have prompted people and institutions across the country to acknowledge and confront enduring forms of racial discrimination.

The letter listed seven grievances and dozens of requests. It called for the agency to publicly acknowledge that systemic racism is a public health crisis, expand internship and fellowship opportunities to students at historically Black colleges and universities, and adopt mandatory implicit bias training.

“Dr. Redfield received the letter and responded,” a spokesman for the agency said in an email, without elaborating on the response. “C.D.C. is committed to fostering a fair, equitable, and inclusive environment in which staff can openly share their concerns with agency leadership.”

Signatories of the June 30 letter, all of whom were employees of the C.D.C., could not be reached or declined to comment. Former staff members said that the current employees would not be allowed to speak to the news media without clearance.

“People are really nervous, which is why I am an intermediary,” said Dr. Camara Phyllis Jones, an associate professor at the Morehouse School of Medicine in Atlanta and a former president of the American Public Health Association.

Dr. Jones worked at the C.D.C. for 14 years before she left in 2014. She was a medical director whose work involved measuring and addressing the impact of racism on national health. The letter rang true for her, she said, adding that toward the end of her tenure at the agency, she felt that her work had been stifled.

She has been in touch with some of the letter’s signatories and said that most of the more than 1,000 people who have signed it so far did so after a smaller group of employees drafted the letter and sent it to Dr. Redfield.

“You have amazing people who are being stifled and thwarted,” Dr. Jones said. “If I were the director, I would receive that letter with immense appreciation and immediately try to start working on it.”

Gregorio Millett, an epidemiologist who left the C.D.C. after 13 years to work for the Obama administration, said that he had good experiences with mentors at the agency. But he said it was common for African-American employees there to feel constrained or ignored.

“I think the C.D.C. should really take this issue far more seriously than it has in the past,” Mr. Millett said. “We need to go beyond listening sessions. It’s time for action. In fact, it’s long overdue.”

He added that Black leaders and scientists at the agency have done groundbreaking work in identifying and addressing the effects of social inequities and structural racism on health in the United States. “There needs to be more individuals of color involved in the leadership at C.D.C.,” he said. “I’ve seen firsthand how that makes a difference.”

As of Tuesday morning, more than 3.3 million people in the United States had been infected with the coronavirus, and at least 135,400 had died, according to a Times database, and the number of new cases has surged in recent weeks. The pandemic has both highlighted and exacerbated racial inequities in the United States.

It has been clear for months that people of color have been disproportionately hurt by the virus. And last week, a set of new federal data — made available after The Times sued the C.D.C. — revealed a more complete picture: From the beginning of the outbreak through at least May, Black and Latino people in the United States have suffered higher rates of infection and death across hundreds of counties in urban, suburban and rural areas, and across all age groups.

“Racism is always important to address,” Dr. Jones said. “But it’s especially important to address if it’s impeding the nation’s response to a pandemic.”

Abby Goodnough contributed reporting.