The discovery of packages containing white powder and addressed to the Australian Christian Lobby (ACL) caused the evacuation of a Canberra mailing centre on Friday morning.

ACT Policing officers attended the Fyshwick building on Thursday night in response to reports of two suspicious packages.

HAZMAT and the ACT Emergency Services Agency conducted tests on the packages, which were sent for forensic examination and deemed to be non-hazardous.

Australia Post confirmed the centre, which is understood to have been occupied by roughly 30 staff at the time, was evacuated for a short time early on Friday morning.

An ACT Policing spokeswoman said police would continue to work with the ACL to investigate the origin of the packages.

ACL managing director Lyle Shelton blamed same-sex marriage advocates for the "act of bullying", though the senders' identity remained unknown.

"I am deeply disturbed that there are elements within the same-sex marriage movement who are willing to incite this sort of behaviour," Mr Shelton said.

"It is intended to intimidate our staff and an attempt to silence us."

About 30 staff at Australia Post's Fyshwick site were evacuated on Friday morning. ( ABC News: Clarissa Thorpe )

He said the packages were the most recent in a string of "threats" directed at the ACL as the same-sex marriage postal survey approaches.

Mr Shelton said in response to death threats aimed at staff and a recent egg-throwing incident at the Deakin headquarters, the group had ramped up security at its offices.

"We have been very respectful in this debate... which should be allowed to to happen with freedom and that should be respected by all sides of the debate," Mr Shelton said.

"This is a debate that should be had with civil discourse, not with white substance, not with intimidating tactics, not with eggs and not with bullying."

Marriage Equality Australia calls for respectful conversation

Co-chair of Marriage Equality Australia Alex Greenwich agreed, saying these kind of tactics had no place in what should be a respectful argument.

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"The matter today is obviously one for police ... [but] in terms of the campaign for marriage equality, we continue to focus on the personal stories of people for whom this reform is important," he said.

"All Australians, regardless of their views on marriage equality, would expect a respectful and dignified debate, one which is focused on the issue at hand and one where all sides are treated respectfully and in a dignified way."

But Mr Greenwhich also levelled blame at the No Campaign for the debate descending to this level.

"We've seen the tactics of the opponents of reform and their misleading and dishonest information," he said.

"They've made it clear that they are not debating the issue of marriage equality, they're looking for every other kind of dishonest distraction that they can."

Other same-sex marriage advocates have expressed concern over "insulting" and "mean-spirited discourse" ahead of the national postal vote on the issue.

Earlier this week Prime Minister Malcolm Turnbull condemned an anti-LGBTI poster spotted in Melbourne. The poster said "stop the fags" and had an image of two hands holding rainbow-coloured belts, as well as a child sitting with its head down.

Mr Turnbull urged all Australians to have a respectful debate and maintained a postal vote on same-sex marriage was the right decision.