The unfair dismissal case of Fern and Rob Messenger against Senator Jacqui Lambie and the Commonwealth resumed in Federal Court on Monday.

Mr Messenger had been Senator Lambie's senior adviser and Mrs Messenger had worked as her office manager before their employment was terminated in May 2017.

Senator Lambie told the hearing about the relationship breakdown that saw her pitted against the two following a fierce altercation between herself and Ms Messenger in June 2016.

The senator sought to enter into mediation with Mrs Messenger after some months when the relationship deteriorated and while her office manager was on sick leave.

She said she was notified in a December email from Mr Messenger that his wife was on leave because of workplace stresses.

On the day mediation was set to occur, Mrs Messenger had visited the office to shred documents in Senator Lambie's absence.

"Mrs Messenger was not well enough to go through any mediation and yet she was in the office shredding documents at the same time," Senator Lambie said.

"Any little bit of trust that was left - I think it was all but over after that."

Senator Lambie said the office environment was completely dysfunctional when the pair was at work.

The office dealt with a large number of complaints from veterans.

Senator Lambie said she was concerned government documents may have been destroyed or sensitive information. Mr Messenger's employment at the time was also brought into question due to complaints from staff about his behaviour.

"There was absolutely no trust left with him and there was too much volatility in the office because of Mr Messenger's conduct," Senator Lambie said.

Mr Messenger and his wife in March 2017 sent a public disclosure document to Prime Minister Malcolm Turnbull with numerous complaints about Senator Lambie.

Senator Lambie said their actions were intended to humiliate and demean her.

"To me, it was 'last straw mate, I'm done'," she said.

The Messengers will cross-examine Senator Lambie on Tuesday.