Members of the British National party (BNP) are being bombarded with phone calls after a list naming them was published on the web.
Party spokesperson Simon Darby told politics.co.uk hundreds of members were receiving phone calls "on an industrial basis" and accused trade union call centres of being responsible.
He said the case was in the hands of the party's solicitors and that "it's not an option for us not to take legal action".
BNP leader Nick Griffin, told the Today programme a senior former employee who left the party late last year was believed to be responsible.
And he added he plans to use the Human Rights Act to pursue the case, despite the party's opposition to the legislation as it originates from the European Union.
The membership list details the employment of those named, including those working in jobs where it is not permitted to be a member of the far-right party like police, soldiers and teachers.
"We take a very dim view of it," Mr Darby added.
"In a way it's complimentary because we're obviously a threat to the political establishment. It'll backfire."
A court injunction bars the publication of the list, meaning the person who was guilty of posting it on internet sites could face jail, Mr Griffin warned this morning.
Mr Darby said he feared "it boils down to elements aligned to Labour".
"It's not just an attempt to intimidate the party," he warned.
"It's an attempt to intimidate the whole population."