National MP Todd Barclay declined to be interviewed by police who were investigating claims he had secretly recorded staff in his electorate office.
Documents show a former long-serving staff member, who had worked in the electorate for 17 years, told police she had been informed Mr Barclay had recordings of private and personal calls from her office.
Mr Barclay initially said he would cooperate with police, but now said he had declined to be interviewed.
"During the process my lawyer was asked by police if I wanted to make a statement. We talked about it and decided to decline the police's invitation, as is my right."
He said it was an employment matter, so he would not give any more details.
Labour Party police spokesperson Stuart Nash said the National MP had set a bad example for the public in not co-operating with police.
At 26, Mr Barclay is the youngest MP.
He entered Parliament in 2014 after taking over the Clutha-Southland seat from Bill English, who has since become Prime Minister.
Mr English said he knew the complainant well, but the matter had been dealt with and it was time to move on.
The police said there was insufficient evidence to prosecute Mr Barclay.