A proposed law change would allow security agents to spy on foreign communications with impunity, including messages to world leaders who will visit New Zealand for next year's Rugby World Cup.

The Security Intelligence Service Bill is expected to be introduced to Parliament tomorrow amid strong opposition to how it is being processed.

The bill will clarify the 41-year-old law outlining how intelligence warrants can be granted. It will specify electronic tracking as well as what the SIS can target, including phones, accounts, emails, computers and IP addresses.

Prime Minister John Key wants the bill passed into law by the start of the Rugby World Cup next year.

One proposed change is that SIS agents would be free from any liability in executing foreign or domestic warrants; at present they are free from liability only while executing domestic warrants.

Green Party MP Keith Locke said the timing suggested that the Government wanted to intercept international communications in time for the arrival of lots of foreign delegations.

But he admitted that the World Cup would draw a limited pool of foreign leaders. "Rugby doesn't have quite the same superpower dimension. The Chinese aren't coming, for example."

A regulatory impact statement suggested that the extra freedom from liability could be balanced by making foreign warrants subject to the approval of the Commissioner of Security Warrants.

Mr Locke said the bill would expand SIS powers.

"In terms of monitoring equipment they have added a few things saying you could install a device, change it and remove it: you can trespass property for a whole lot of things connected to the device."

Meanwhile, Labour leader Phil Goff has called for the hearings on the bill to be public, citing a precedent in 1999.