The families of 17 service members killed in the line of duty on Monday demanded Donald Trump apologize for attacking the Khan family, saying his remarks are “cheapening the sacrifice made by those we lost.”

In a letter addressed to the GOP nominee, the Gold Star families, a military distinction for those who have lost a family member in the line of duty, called Trump’s attacking the Khans “repugnant and personally offensive.”

“When you question a mother’s pain, by implying that her religion, not her grief, kept her from addressing an arena of people, you are attacking us,” they wrote. “You are not just attacking us, you are cheapening the sacrifice made by those we lost.”

The letter continued: “This goes beyond politics. It is about a sense of decency. That kind decency you mock as ‘political correctness.'”

After Khizr Khan delivered a powerful speech at the Democratic National Convention on Thursday, Trump has repeatedly attacked Khan and his wife, Ghazala.