A mail centre in Canberra was evacuated this morning after white powder was discovered in packages addressed to the Australian Christian Lobby (ACL).

According to the Sydney Morning Herald, police and emergency services attended the scene. Tests proved the material to be harmless and the centre reopened.

A spokesman for Australia Post said: 'Australia Post takes the safety of all of our staff extremely seriously. Relevant authorities evacuated the Canberra Mail Centre early this morning following the detection of a suspicious mail item.'

The ACL is in the forefront of a divisive battle about same-sex marriage, to which it is passionately opposed. A referendum on the issue is due to conclude in November.

Managing director Lyle Shelton told Fairfax Media: 'This is obviously of great concern. We have been receiving packages of glitter all week, which we have not opened, and we have had individual people online encouraging people to send in noxious substances. We have reported that to the federal police.

'We think this should be a respectful debate [about changing same-sex marriage laws], but in the last 12 months we have endured death threats, there has been a car bomb exploded outside our office, our office has been egged and we have been mailed all of this glitter.

'This is part of what would seem to be a way to try and intimidate us into silence.

A car bomb exploded outside ACL's headquarters in December last year. No one was injured and police have said the alleged offender, Jaden Duong, intended to commit suicide by blowing himself up. They said his actions were 'not politically, religiously or ideologically motivated'.