Ten thousand protesters march on Parliament in 1977 to oppose spy law reforms many feared would turn the country into a police state.

Fears that New Zealand could become a totalitarian police state prompted 10,000 people to march on Parliament in 1977, as politicians moved to increase spies' powers.

Surveillance warrants without expiry dates, spooks immune to prosecution, and public servants being forced to spy on fellow citizens were among changes that inflamed opponents of Security Intelligence Service Act reforms. Not only espionage but political "subversion" would now be targeted by the SIS, and its director could order surveillance without prior approval from a security council.

"Terrorism is a growing and frightening phenomenon," National prime minister Robert Muldoon said in defence of the changes.

The public disagreed. Protesters crammed Parliament's public galleries as MPs debated the bill on October 18. Muldoon was unleashing "weapons of fascism", one protester screamed before singing the national anthem and throwing a New Zealand flag into the debating chamber.

In the largest eviction witnessed in the House for three decades, 150 people were forcibly ejected at Muldoon's request, many of them kicking and screaming.

"I hope you get a kick out of this, Muldoon and you National Party bastards," a woman shouted as she was carried out, The Evening Post reported.

The SIS was formed in 1956 at the height of the Cold War, but in the 1970s had come under criticism for several bungled operations. Suspected Soviet spy Bill Sutch had his home bugged and searched, Muldoon used SIS intelligence to undermine trade union, and secret information was leaked about the alleged sexual activities of Labour MPs Gerald O'Brien and Colin Moyle.

"Unfortunately we know from recent events that information secretly and unlawfully obtained may be employed recklessly to persecute political opponents," Victoria University professor John Roberts told the Post.

A Labour-ordered investigation into the SIS formed the basis for Muldoon's reforms, although opponents argued National went far beyond what ombudsman Guy Powles had recommended.

On October 10, 2000 protesters gathered at the Opera House in a rally organised by Roberts to condemn the "grave attack on democratic rights of New Zealanders".

Muldoon's attempt to force public servants to assist in SIS investigations was slammed by Public Service Association president Jim Turner. "Warrants could be issued for teachers to spy on pupils, or nurses and doctors to spy on patients," he told the crowd.

On October 14, 10,000 opponents massed at Parliament, then marched to the SIS headquarters on Taranaki St, where demonstrators threw paint bombs and oranges.

Busloads of police officers and detectives surrounded the SIS building shoulder to shoulder after a protester broke a window by throwing a placard pole.

The protest dispersed soon afterwards, and Muldoon's spy laws were passed. The legislation has been amended every decade since, during which time the SIS's powers have further increased.