A senior Customs manager told New Zealand Immigration officials months before a raid on Kim Dotcom that feeding the FBI information about the internet businessman would buy them "many brownie points".
Emails released under the Official Information Act show the manager, Gary Davis, giving this advice to Immigration New Zealand's Intelligence Unit in September 2011.
The Government's spy agency began monitoring Mr Dotcom three months later in preparation for the January 2012 raid on his mansion near Auckland on behalf of the FBI.
Customs refused to make any comment about the emails on Tuesday. It said Mr Davis is no longer the operations manager of Customs' then newly-opened Integrated Targeting Operations Centre. He is now its operations manager for intelligence.
Green Party MP Steffan Browning has seen the emails and told Radio New Zealand's Checkpoint programme on Tuesday it suggests a culture of free exchange of information from Customs without a formal legal request.
"To be prepared to dish out something on a New Zealand resident when there was no formal legal request is pretty concerning because it could be on you, it could be on me, it could be on anybody."
Immigration New Zealand said it has no record that any information was passed on to the FBI following the email exchange.