Police officers and staff could face dismissal if they join the British National Party (BNP) under a new policy agreed by senior officers.
Police officers and staff have been banned from joining the BNP
The Association of Chief Police Officers (Acpo) said the policy was unanimously endorsed at a Chief Constables' Council meeting this month.
The policy applied to membership of bodies in conflict with the force's duty to promote race equality, it said.
But the BNP says it is a legal party, and that Acpo's policy is undemocratic.
In a statement announcing the policy Acpo president Chris Fox said chief police officers were totally committed to compliance with the Race Relations Amendment Act 2000.
He said he was "extremely pleased" to be able to take that compliance further.
Mr Fox said: "Under this policy, no member of the police service, whether police officer or police staff, may be a member of an organisation whose constitution, aims, objectives or pronouncements contradict the general duty to promote race equality.
"This specifically includes the British National Party.
"We anticipate that non-compliance will result in dismissal," he added.
But BNP national press officer Phil Edwards said "plenty" of serving police officers were already members of the party.
The BNP, he said, was strongly in favour of law and order and supported "the plight of the ordinary police officer within the liberal society".
"There's an anomaly if we support all that and they don't want the coppers to be members. It's a sham.
"We live supposedly in a democracy and they're telling people that they can't be a member of this legal political party - this shows the hidden hand of anti-democratic forces," Dr Edwards said.
Acpo head of race and diversity and Leicester Chief Constable Matt Baggott dismissed the BNP's claim as "immaterial".
He said the police had an overriding legal duty to promote race equality and retain public confidence.
Nationwide, police would be banned from being a BNP member and any existing officers reported as members would be investigated, he said.
"It is going to be immensely reassuring for the public in a very mixed community like Leicester, and for the vast majority of colleagues, that we mean business," he said.