The prisoner, Valeriece Ealom, has complained that staff at the Leavenworth Detention Center have repeatedly disparaged her wearing of a headscarf, calling it a “rag” and have ordered her to take it off before being allowed to leave her cell.

Muslim Advocates, a civil rights and legal advocacy group based in Washington, D.C., said in a letter made public Wednesday that it was concerned about Ealom’s treatment.

The letter was addressed to CoreCivic, the Tennessee-based company that operates the prison, and the U.S. Marshals Service, which contracts with CoreCivic to house federal prisoners.

“While LDC’s management has been aware of her mistreatment, they have failed to take any meaningful corrective action and USMS has likewise permitted this harassment to continue for months,” the letter said.

Leavenworth Detention Center has faced many complaints in recent years. The prison is the focus of ongoing legal action over the taping of phone calls between prisoners and their lawyers. A Justice Department audit last year blasted the prison for understaffing, security problems and deceptive practices. Prison officials have been accused of retaliating against employees who complain.

Ealom, 49, has been held at the facility since last November after federal prosecutors moved to revoke her parole.

“Like many Muslim women, Ms. Ealom believes it is her fundamental obligation to practice modesty by wearing a headscarf,” the letter said.

A prison chaplain provided Ealom with a headscarf to wear. But when other employees allegedly harassed Ealom about wearing it and threatened to discipline her if she did not take it off, Ealom filed a formal complaint.

That only made the harassment worse, the letter says.

In January, Ealom alleges, she was told she would be put in solitary confinement if she did not remove the scarf before leaving her cell.

As a result, she missed receiving her prescribed medication that day.

When Ealom complained about that, one officer confiscated her scarf as “contraband,” the letter says.

Other times, a guard has interrupted her prayers to conduct searches of her cell.

In February, acting without a lawyer, Ealom filed a federal civil lawsuit over her treatment.

A judge dismissed the suit in June, saying that it did not provide enough information to show how she had been harmed.

In Wednesday’s letter, Muslim Advocates says that CoreCivic and the Marshals Service must immediately take steps to remedy the situation, which it argues is a violation of federal law.

“Despite being aware of the officers’ bigoted and discriminatory conduct, LDC’s management has not taken any meaningful steps to address the situation,” the letter said.

CoreCivic did not immediately respond to questions about Ealom’s claims.