Labour leader Andrew Little is accusing the Prime Minister of being tricky when discussing the activities of the Government Communications Security Bureau (GCSB).
John Key is not ruling out the GCSB being involved in the mass collection of data but insists it does not do mass surveillance.
Mr Key said when he offered to resign as Prime Minister that related solely to claims the GCSB engaged in mass surveillance.
Mr Key was asked, in that case, to explain the difference.
"They don't undertake mass surveillance of New Zealanders. There is no, sort of, new terms here. I don't even know what you mean by mass collection. I've no clue - it's not a term I've ever seen, it's not a term I've ever used."
The NSA documents cited by Edward Snowden referred to the GCSB undertaking what was described as full-take collection from 2009.
Mr Key was asked whether that could mean mass collection.
"Look, I think you're just winding yourself into knots, which are a complete waste of time. They're circular arguments. Go back to the simple question - do we have a warrant and is that warrant legal?"
Mr Little said Mr Key was using semantics to avoid answering straightforward questions about the actions of the spy agency.
"The Prime Minister's being pretty tricky about the difference between data collection and then private and surveillance. I think he needs to be clear with New Zealanders about what that difference is. He says that you can go to any lawyer and get a different opinion. He's got the country's top lawyer, the Attorney-General."
The GCSB and its sister agency the Security Intelligence Service (SIS) are due to appear before Parliament's Intelligence Committee for their annual review tomorrow morning.