Information Commissioner Elizabeth Denham has singled out UKIP as one of four organisations appealing against a notice to give evidence to the ICO's Information Rights Tribunal.
Denham is investigating the use of data analytics for political purposes and has called on more than 30 organisations - including all the major political parties in the UK, as well as organisations offering data to aid their campaigning - to give evidence.
"Among those organisations is AggregateIQ, a Canadian-based company, used by a number of the campaigns," Denham wrote.
Denham describes the investigation as being "designed to examine how personal information was analysed to target people as part of political campaigning and have been particularly focused on the EU Referendum campaign".
She added that some organisations have been co-operative, while suggesting that others have been harder to work with, implying that UKIP fell into the latter category.
"A number of organisations have freely co-operated with us, answered our questions and engaged with the investigation. But, others are making it difficult.
"In some instances we have been unable to obtain the specific details of work that contributed to the Referendum campaign and I will be using every available legal tool and working with authorities overseas to seek answers on behalf of UK citizens.
"Other organisations have failed to be as comprehensive as I believe they need to be in answering our questions and have forced us to invoke our statutory powers to make formal demands for information.
"The ICO has issued four information notices as part of the investigation including one to UKIP, who have now appealed our notice to the Information Rights Tribunal."
Describing the investigation as a "high priority" for the ICO, Denham explained that its purpose is to ask "whether there was a legal basis to use this information. Did people have a way of exercising their privacy rights?"
The Electoral Commission is also examining funding associated with the Referendum and will work with the ICO on this case.
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