Spy watchdog Cheryl Gwyn will investigate allegations New Zealand's intelligence agency was used to influence Trade Minister Tim Groser's bid to become boss of the World Trade Organisation.

Groser failed to get the job despite allegations the Government Communication Security Bureau used an internet surveillance system to intercept emails about candidates from Mexico, Brazil, Jordan, and Kenya.

The New Zealand Herald revealed the scandal based on documents provided by whistleblower Edward Snowden.

The minister in charge of the GCSB at the time was Prime Minister John Key.

Gwyn says the activity of the GCSB gathering foreign intelligence is of sufficient importance for the inquiry.

Gwyn says while it's unlikely she'll be able to confirm or deny specific spy allegations, she can look at the GCSB's activities and whether they worked within their mandate.

She also plans to look at whether spies maintained their political neutrality.

When asked to comment on the matter, Groser's office refused to grant an interview, or make a statement.