The letter, signed by Federal Railroad Administration head Amit Bose, came after the agency inspected the company’s East Departure Yard in North Platte, Nebraska, this summer and found that more than 70% of the train engines had safety defects, as did 20% of the cars — defect ratios twice the national average. Conditions didn’t improve when inspectors returned and found locomotives with defects still in use. “We haven’t been able to get to them yet,” a Union Pacific director said, according to the letter.

The company “has not displayed a sense of urgency to improve locomotive and car conditions,” the letter said.

The revelation comes as the safety record of the country’s railroad industry is under deep scrutiny. All eyes have been on Norfolk Southern, whose train notoriously derailed in East Palestine, Ohio, in February, releasing toxic pollution and forcing a mass evacuation. But just one month later, Union Pacific had its own accident. A runaway train carrying iron ore reached a reported 118 mph before it derailed in Kelso, California. No one was injured.

Transportation Secretary Pete Buttigieg has been trying to get the nation’s largest freight rail companies, the so-called Class 1s, to participate in a voluntary safety program in which workers can confidentially report “close calls” like runaway trains and misaligned switches without fear of retribution; NASA would process submissions, as it does for a similar program that governs the aviation industry.

The rail industry has resisted, saying employees could use the system to avoid punishment for their own safety violations. In a slight departure from the other big companies, a spokesperson with Union Pacific said it is more concerned that the system could delay how quickly the company addresses safety problems.

The company, which is the largest railroad in the world, said in a statement that safety is its first priority and that it wouldn’t compromise the safety of its staff. “There is no correlation between recent furloughs and Union Pacific’s ability to address mechanical repairs,” the statement said, adding that the company has appropriate staffing. The statement went on to say that Union Pacific will address the concerns raised in the letter and that it respects the federal inspectors. The company will be sending a formal response.

Labor union leaders said the safety problems flagged at Union Pacific are the natural byproduct of a business model adopted by the train companies called precision scheduled railroading. As ProPublica reported earlier this year, it places an emphasis on efficiency, running heavier, longer trains with leaner staffs and keeping them in constant motion.

“Until these railroads say they are done with PSR, this is what we’re going to get,” said Randy Fannon, a national vice president for the Brotherhood of Locomotive Engineers and Trainmen. “There’s no community safe from these defects and dangerous situations. UP will have their East Palestine soon unless they correct these issues and return to a normal maintenance program.”

According to the letter, federal inspectors got numerous calls from Union Pacific managers, including high-ranking company officials, requesting that they leave the yard because they were slowing down business. Under the Trump administration, inspectors might have complied, said Jared Cassity, the alternate national legislative director at the International Association of Sheet Metal, Air, Rail and Transportation Workers, known as SMART. He called the federal letter “absolutely terrifying.”

“It just speaks to the fact that [company-based] inspections are not being done in a meaningful way. And the fact that Union Pacific is furloughing is only doubling down on the status of our equipment and just how dangerous it really is,” Cassity said. “They’re spitting in the face of railroad safety.”