Australians are receiving unauthorised same-sex marriage postal survey campaign material, including leaflets from the no campaign’s Coalition for Marriage, despite a new law requiring materials to identify their source.

After we asked readers to submit misleading survey material, Guardian Australia has continued to receive complaints of unauthorised material, even after the safeguards law came into force on 14 September.

These ranged from leaflets that identify they are from the Coalition for Marriage but lack further details, to anonymous leaflets warning that marriage equality will lead to gender fluidity and “child abuse” such as hormone therapy, and a Facebook post urging a no vote depicting Christ in chains.

Electoral experts, including Prof Graeme Orr, from the University of Queensland, and a former Australian Electoral Commission official, Michael Maley, have warned that authorisation provisions may be difficult to enforce unless people are caught distributing anonymous so-called “shit sheets”.

The Coalition for Marriage “3 ways gay marriage will affect your family” leaflet was distributed with other unaddressed junk mail in Forestville, South Australia, at the weekend. It claims marriage equality will lead to “radical gay sex education”, “weaponise federal and state anti-discrimination law” and prevent churches and schools from teaching their beliefs.

The new law requires paid advertisements, printed material and material intended to affect whether a person provides a response to the survey or the content of the response to be authorised. Breach of the provision can lead to a “civil penalty” of up to $25,200.

The leaflet includes the URL of the Coalition for Marriage website, which says it is authorised by “L Shelton” and includes a postal address, details Orr said should be disclosed on the leaflet itself if sent after the new law came into force.

The Coalition for Marriage ‘3 ways gay marriage will impact your family’ leaflet distributed in Forestville, South Australia, on Sunday

The Coalition for Marriage makes the leaflet files available on its website for download and distribution by anyone. While the English-language pamphlets now have authorisation details on them, foreign-language pamphlets do not.

Guardian Australia contacted the Coalition for Marriage and the Australian Christian lobby for comment.

Guardian readers have reported other material with no authorisation details.

One reader submitted a photo of a leaflet titled “10 reasons to vote no in the marriage plebiscite”, and said it had been received some time between 19 and 22 September. The leaflet said only that it was “sent to you by a member of the deeply concerned and silenced majority”.

The leaflet claims marriage equality will lead to “a raft of gender fluidity laws that will impact the opinions we are permitted to hold, what we say and what we do, and what schools must teach (eg radical queer theory via Safe Schools propaganda)”.

The issue is not limited to printed material. Guardian Australia has been sent details of Facebook ads in the form of “sponsored posts” that do not have any authorisation, including some that link to homophobic material which we have chosen not to publish.

One post from the Facebook page titled This Is Christian Australia was originally posted on 27 August but was promoted as a sponsored post as recently as Thursday, according to one reader who saw the post in their feed.

A sponsored ad from the Facebook page This is Christian Australia Photograph: Facebook

“When you are on your knees begging for mercy; the Lord will reply ‘but you voted for this’,” it warns. “Vote no for gay marriage and worship the Lord to bless your family.”

Neither the post nor the Facebook page contains any details on who might have authorised the ad.

The AEC commissioner, Tom Rogers, told a Senate committee on Friday the authorisation requirement was not retrospective, meaning it did not apply to material published before the law. He said social media posts may need to be authorised where “further sharing is paid for” after 14 September.

The co-chair of the Equality Campaign, Anna Brown, said it was “deeply concerned about the increasing amount of unauthorised anti-LGBTI no material and it’s content”.

“These materials are impacting on LGBTI people, their friends and families. All Australians would find this unacceptable,” she said, citing a 40% increase in demand for helplines for LGBTI people in the Past few weeks.

The Equality Campaign has already complained to the AEC about an unauthorised robocall it believes is push-polling because it claims same-sex marriage will lead to “radical gay sex education”.

The Anglican dean of Darwin has complained to the AEC about unauthorised anti-marriage equality emails “full of homophobic dog whistles”.

Maley said where authorisations were left off inadvertently, the issue could be rectified easily after a complaint to the AEC. But Orr said enforcement of authorisation laws for anonymous material had always been difficult.

“If someone is willing to put out anonymous material they are not going to put the name or the printer on it or they will put a false name,” Orr said.

“Short of CCTV, a tipoff dobbing them in or catching them in the act distributing it, it’s very difficult to enforce.”

Orr noted the safeguard law set a three-month time limit on all prosecutions, meaning aggrieved campaign organisations, the AEC and police would have until mid-February to investigate and prosecute alleged breaches.

Orr said it could take “many months ... to track down some of the more egregious material” using techniques including cyber forensics to probe the IP addresses hosting websites.

But if the survey material was considered electoral material the AEC could still have jurisdiction even after the limitation period, he said.

Maley said “nasty” material circulated in letter boxes was “deliberately anonymous … because it’s stuff people are ashamed to put their names to”.

“You can go to authorities with the piece of paper and the lack of authorisation is obvious, but not who has distributed it. If people want to do very dirty stuff, particularly in hard copy, there is very little you can do unless you catch them in the act.”

We will continue to monitor campaign material throughout the survey period. Please continue to share material – either on social media, or in leaflets and pamphlets – by following this link.