(Reuters) - U.S. railroad Union Pacific ( UNP ) interfered in a federal safety audit after employees were coached in how to respond, prompting the rail agency to end the review, the chair of the Senate Commerce Committee said Friday.

Senator Maria Cantwell said she wants answers about Union Pacific's ( UNP ) actions after the Federal Railroad Administration told the committee this month it had been was forced to discontinue its assessment "due to Union Pacific's ( UNP ) actions to undermine the integrity of the assessment process," Cantwell said.

She asked the company to provide all documentation regarding the safety culture audit, along with current policies and plans to improve its safety culture. Union Pacific ( UNP ) did not immediately respond to a request for comment.