Transparency advocates have criticised Facebook for changes that make it harder for Australian not-for-profits and journalists to monitor political advertising on the platform just months out from the federal election.

Facebook has made repeated pledges to shed greater light on the way politicians and interest groups use the medium to tailor and target advertising to specific individuals.

But it was revealed on Monday that Facebook had restricted the ability of external transparency campaigners to collate and scrutinise ads.

One of the affected groups, the US-based not-for-profit investigative journalism outfit ProPublica, said a tool it had developed to help monitor Facebook political advertising had been restricted in a wider crackdown on third-party plug-ins accessing unauthorised data from its site.

ProPublica’s tool is used by organisations in Australia – including Guardian Australia – to monitor the way political advertising is being deployed. In 2017, Guardian Australia used the ProPublica tool to reveal how Clive Palmer’s United Australia party, the Liberal, Greens and Labor parties, unions and not-for-profits had paid Facebook to push content into users’ feeds.

Such ads would have otherwise been largely hidden from the general public, only visible to those who had been deliberately targeted.

Transparency International, which is this week preparing to release its report on how Australians perceive government corruption, said the timing of the recent changes was particularly poor, given the proximity to the federal election.

“It does certainly show poor judgment in the lead-up to the election, where the community is going to be very interested in the broader issues around transparency, accountability, and strengthening parliamentary standards,” Transparency International’s chief executive, Serena Lillywhite, said. “We should be able to see freely and openly and in real time exactly what advertising is being done for political purposes on Facebook and what the links may be in trying to attract political donations.”

The recent changes were designed to crack down on third-party plug-ins – ad blockers, for example – accessing data from the platform in unauthorised ways. A Facebook Australia spokesman said the changes were part of a “routine update”.

“We regularly improve the ways we prevent unauthorised access by third parties like web browser plug-ins to keep people’s information safe,” the spokesman said. “This was a routine update and applied to ad blocking and ad scraping plug-ins, which can expose people’s information to bad actors in ways they did not expect.”

Facebook’s treatment of targeted advertising came under intense scrutiny following the Cambridge Analytica scandal. It has since flagged significant restrictions on political advertising. In some countries, it released searchable public databases of political ads late last year. It is unclear whether this will be deployed in Australia and, if so, whether it will be available before the federal election.

Facebook has taken other steps to improve transparency and integrity around political advertising. It has attempted to proactively identify and take down fake accounts and spam, improve transparency around pages and their current ads, and has increased its community operations team to 30,000 people. The company has also established a “war room” to help safeguard the integrity of the platform, made up of 24 experts in a range of areas, including software engineering, threat intelligence, data science, and legal.