The UK's data privacy chief has joined the chorus of warnings over Facebook's proposed digital currency, Libra.
Elizabeth Denham, who runs the Information Commissioner's Office, has signed a statement alongside counterparts in the US, Canada, Australia and the European Union.
The statement said they have "shared concerns" over "privacy risks posed".
Banking chiefs, regulators and US President Donald Trump have also expressed doubts about the currency.
Monday's statement from the privacy chiefs calls on Facebook to provide more details about how the tech giant will protect user data.
Libra, and its digital wallet Calibra, were announced in June by a group of companies backing it, led by Facebook.
Ms Denham said: "The ambition and scope of the Libra project has the potential to change the online payment landscape, and to offer benefits to consumers.
"But that ambition must work in tandem with people's privacy expectations and rights.
"Facebook's involvement is particularly significant, as there is the potential to combine Facebook's vast reserves of personal information with financial information and cryptocurrency, amplifying privacy concerns about the network's design and data-sharing arrangements."
She said that, while Facebook has opened talks with financial regulators, there was little detail about how the social media company will handle customer information. Data protection must be a key part of the dialogue over Libra.
The joint statement has also been signed by data protection authorities in Albania and Burkina Faso.
It said: "As representatives of the global community of data protection and privacy enforcement authorities, collectively responsible for promoting the privacy of many millions of people around the world, we are joining together to express our shared concerns about the privacy risks posed by the Libra digital currency and infrastructure.
"Other authorities and democratic lawmakers have expressed concerns about this initiative. These risks are not limited to financial privacy since the involvement of Facebook Inc and its expansive categories of data collection on hundreds of millions of users raises additional concerns."
Libra has already faced direct scrutiny in the US Congress.
Last month, Libra chief David Marcus, told the Senate Banking, Housing and Urban Affairs Committee he understood "loud and clear" that people do not want financial details connected to their social media data.
"I know we have to earn people's trust for a very long period of time," Mr Marcus said.
US Treasury Secretary Steven Munchin and Federal Reserve chairman Jerome Powell have voiced their concerns, and Mr Trump tweeted that he is "not a fan".
Bank of England Governor Mark Carney cautiously welcomed the digital currency, saying the Bank "approaches Libra with an open mind but not an open door".