A feedback letter from the Care Quality Commission (CQC) to the trust said a recent inspection found “concerns over culture” at the hospital emergency department.
The CQC said: “We spoke to several staff who told us they perceived there was bullying among their colleagues.”
An unannounced inspection was carried out by inspectors in June at both Lincoln and Boston hospital sites.
A formal report is expected to be published by the CQC at a later date.
Dr Neill Hepburn, medical director of ULHT, said bullying was “unacceptable” and that the trust takes the concerns seriously.
“This is something we take very, very seriously and we will work to understand it and address it more effectively,” he said.
“We have a zero tolerance to bullying, it’s just totally unacceptable.
“Sometimes it may happen because of poor training and poor competence. Some individuals are able to improve and sometimes they are not, in which case we have no role for them.”
He added that staff who have concerns should escalate it through their line manager or speak to the trust’s Freedom to Speak Up Guardian who is independent of management.
Meanwhile, Michelle Rhodes, director of nursing, told councillors on the health scrutiny panel for Lincolnshire that the trust was “disappointed” with the findings.
“We were mortified about this particular department in regards to bullying, they have always had a really good team in there,” she said.
“We are doing quite a lot of work around values across the trust in its entirety.”
Coun Carl Macey, chairman of the health scrutiny panel, said that dealing with bullying within the trust needed to be done in an “easier manner”.
“It was quite surprising to hear that there was this issue that had been highlighted by the CQC,” he said.
“We have been told on multiple occasions now that they are dealing with this and that they are moving in the right direction.
“That is obviously not what is being fed back through to us and we want to ensure that those who are working within the trust are not facing these issues.”