Two people have been charged under the Data Protection Act after a British National Party membership list was leaked onto the internet.
Dyfed-Powys Police said a 27-year-old man and a woman, aged 30, were due to appear at Nottingham Magistrates' Court on September 1.
The woman is understood to be Sadie Graham, who was expelled from the far-right party in late 2007 after falling out with its leadership.
The BNP called for a police investigation last November after the names, addresses and contact details of some 10,000 of its members were published online.
Party leader Nick Griffin lodged a complaint with Dyfed-Powys, his local force, on the grounds that publishing the list breached human rights and data protection laws.
He described the publication as "a disgraceful act of treachery" by former BNP staff members who were subsequently sacked.
At the time the BNP said the leak was based on its 2007 membership list, although a number of names of people who were not members had been added.
The list, which included details of some members' jobs, was reported to include serving and former police officers as well as members of the armed forces.
In a statement, Dyfed-Powys Police said: "We can confirm that the two people arrested as part of a joint investigation with Dyfed-Powys Police and the Information Commissioner's Office in relation to alleged criminal offences under the Data Protection Act have been charged with Section 55 Data Protection Act offences.
"The arrests followed an investigation into a complaint received about the unauthorised release of the BNP party membership list."
