Union Pacific managers undermined the U.S. government’s efforts to assess safety at the railroad in the wake of several high-profile derailment, federal regulators say.

Federal regulators say Union Pacific managers undermined their efforts to assess safety at the railroad by coaching employees on how to respond and suggesting they might be disciplined

The Federal Railroad Administration has discontinued efforts to gather information for an assessment of Union Pacific’s safety culture, telling the railroad it found indications of activities by the railroad that “adversely impact the integrity” of the process.

Employees were coached and threatened as Federal Railroad Administration inspected the 23-state rail network after derailments, the agency says.