Britain's data watchdog intends to fine Facebook £500,000 for two breaches of the Data Protection Act.
The Information Commissioner's Office (ICO) said the social media giant broke the law by failing to safeguard people's information and failing to be transparent about how people's data was harvested by others.
Despite the proposed fine being a record for the watchdog, campaigners said it was "unacceptable", as under new GDPR data laws the penalty could have been hundreds of millions.
Data harvested from around 87 million people
Facebook, with CA, has been the focus of the ICO's investigation since February when evidence emerged that an app had been used to harvest the data of 50 million Facebook users around the world.
The total is now estimated at 87 million, the ICO said.
In March 2017, the ICO began looking into whether personal data had been misused by campaigns on both sides of the UK's 2016 EU referendum.
It later launched an investigation that included political parties, data analytics companies and major social media platforms.
The progress report on Wednesday gave details of some of the organisations and individuals under investigation, as well as enforcement actions so far.
Facebook has a chance to respond to the Commissioner's Notice of Intent, after which a final decision will be made.
Criminal action against Cambridge Analytica owner
As well as the proposed fine, the regulator also announced a criminal prosecution of SCL Elections (the parent company of CA) for allegedly failing to comply with an enforcement notice.
The ICO had ordered the company to allow an academic to access the data it held.
SCL Elections was liquidated in the wake of the scandal.
Other regulatory action set out in the report includes warning letters to 11 political parties and notices compelling them to agree to audits of their data protection practices.
Information Commissioner Elizabeth Denham said: "We are at a crossroads.
"Trust and confidence in the integrity of our democratic processes risk being disrupted because the average voter has little idea of what is going on behind the scenes.
"New technologies that use data analytics to micro-target people give campaign groups the ability to connect with individual voters.
"But this cannot be at the expense of transparency, fairness and compliance with the law.
"Fines and prosecutions punish the bad actors, but my real goal is to effect change and restore trust and confidence in our democratic system."
Facebook ‘should have done more’
Erin Egan, chief privacy officer at Facebook, said: "As we have said before, we should have done more to investigate claims about Cambridge Analytica and take action in 2015.
"We have been working closely with the ICO in their investigation of Cambridge Analytica, just as we have with authorities in the US and other countries. We're reviewing the report and will respond to the ICO soon."