OMAHA, Neb. (AP) -- Union Pacific managers undermined the U.S. government's efforts to assess safety at the railroad in the wake of several high profile derailments across the industry by coaching employees on how to respond and suggesting they might be disciplined, federal regulators say.

The meddling was so widespread across Union Pacific's 23-state network that the Federal Railroad Administration had no choice but to suspend its safety assessment of the company, the agency's chief safety officer, Karl Alexy, told Union Pacific executives in a letter dated last week that labor groups posted online Tuesday.

The company indicated Wednesday that the issue was limited to one department. Its president told FRA in a response letter that Union Pacific"did not intend to influence or impede the assessment in any way."

The agency launched safety assessments of all major railroads in the U.S. at the urging of congressional leaders after Norfolk Southern's disastrous February 2023 derailment in eastern Ohio, and the episode with Union Pacific may prompt lawmakers to finally act on stalled railroad safety reforms.

"FRA has discovered that numerous employees were coached to provide specific responses to FRA questions if they were approached for a safety culture interview," Alexy wrote. "Reports of this coaching span the UPRR (Union Pacific railroad) system and railroad crafts. FRA has also encountered reluctance to participate in field interviews from employees who cite intimidation or fear of retaliation."

The chief of safety at the nation's largest rail union, Jared Cassity, noted that the FRA is so small that it must rely on the railroads to police themselves and report safety issues.

"To think that a company the size of a Union Pacific is willing to go to great lengths to intimidate and harass their employees, so that they're not honest in their assessment of a company's safety culture. That begs the question of what else are you covering up?" said Cassity, who is with the International Association of Sheet Metal, Air, Rail and Transportation Workers' Transportation Division, also known as SMART-TD.

A Union Pacific spokeswoman said the railroad believes regulators' concerns center on a message that one manager sent out to employees in his department across the railroad with a copy of the questions FRA planned to ask to help prepare them for an interview.

"The steps we took were intended to help, not hinder, and were taken to educate and prepare our team for the assessment ethically and compliantly," Union Pacific President Beth Whited said in a response letter to the FRA on Tuesday. "We apologize for any confusion those efforts caused."

Last year, the FRA found a slew of defects in Union Pacific's locomotives and railcars after sending out a team of inspectors, and the agency is still working to nail down what caused a railcar to explode in the railroad's massive railyard in western Nebraska.

Democratic Ohio Sen. Sherrod Brown, who cosponsored the bipartisan railroad safety bill after the East Palestine derailment, called Union Pacific's meddling "unacceptable."

"The big railroads keep fighting efforts to improve safety," Brown said. "We need much stronger tools to stop railroad executives from putting their own profits and greed ahead of basic safety."

Brown pledged to fight for a vote in the Senate soon on the bill that would set standards for trackside detectors and inspections that are supposed to catch problems before they can cause a derailment along with other changes. The House has yet to take up a railroad safety bill because Republican leaders wanted to wait until after the National Transportation Safety Board's final report on the East Palestine derailment that's expected in late June.

Whited told the Federal Railroad Administration that Union Pacific plans to launch an internal safety assessment this month, as the agency suggested, because "our goal is to be the safest railroad in North America, a place we know we can get to even more quickly with the FRA's assistance. "

But Cassity said he doubts an internal survey would be accurate because many Union Pacific workers are afraid to speak out about safety concerns. He said the prevailing attitude seems to be "move the freight at any cost," making another major derailment all the more likely.