Local authorities in the Netherlands are using social media for large-scale snooping on citizens, new research has found.
The study says some civil servants had used fake accounts to monitor local Facebook and Twitter pages.
It is suggested that the authorities were seeking to maintain public order and forecast any protests planned online.
Dutch law states that only police and intelligence services can spy on citizens under strict conditions.
The Netherlands' interior ministry has confirmed they are working with local authorities to investigate the reports.
"I am taking this very seriously," said Interior Minister Kajsa Ollongren, "the privacy of citizens is of course paramount."
The research was conducted by the NHL Stenden University of Applied Sciences and Groningen University and is based on a questionnaire of 156 of 352 Dutch municipalities.
Nearly one in six of those surveyed said they had used fake accounts to secretly follow local groups and accounts on platforms such as Facebook and Twitter.
One local official said they had covertly joined private Facebook groups during the refugee crisis to see "what was going on".
According to the research, municipal officials were often unaware that they were breaking the law.
More than half of the civil servants surveyed (54%) also indicated that their local authority did not have a clear policy for online monitoring. This was particularly found in small and medium-sized municipalities.
Moreover, around one-third of the local authorities did not involve a data protection officer in their online monitoring, even though this is required under Dutch law.
Dutch politicians have sounded the alarm about the research findings and online privacy.
Speaking in Parliament on Tuesday, Ollongren acknowledged that the level of knowledge in some municipalities was "at least below par".
"We now know that there is actually no clear picture of what is monitored online by municipalities and of what may be monitored online by municipalities," Ollongren said.
"There is also a clear lack of knowledge about privacy guarantees [which] I think is risky."
The Interior Ministry stated that they would be investigating the matter alongside the Association of Netherlands Municipalities (VNG).
The probe will speak with local authorities in order to "remove these ambiguities", Ollongren said.
The research did not name which Dutch municipalities had used fake accounts to illegally spy on their citizens.
In a statement to The Cube, Euronews' social media newsdesk, local authorities in the capital city, Amsterdam, confirmed they would be co-operating with the national investigation.
"We're investigating where online monitoring takes place in our organisation, with which purpose and how it takes place," an Amsterdam spokesperson said.
"Minister Ollongren and the VNG will investigate this on a national level, we will also participate in this investigation."
The Dutch Interior Ministry has reiterated that the online monitoring of citizens is permitted under limited circumstances under the country's Municipalities Act.
"Tracking citizens to protect public order is only allowed if it complies with privacy legislation and if it complies with our Constitution," Ollongren told Parliament on Tuesday.
"No one from a government can just follow citizens. The police are also not allowed to just follow civilians."
"Article 162 ... does provide a legal basis for non-systematic monitoring, provided that the government makes itself known."