The Royal Mail has refused to carry a Britain First election leaflet that it considers to be illegal.
The leaflet has been produced as part of the far-right group's campaign for the Rochester and Strood by-election.
On one side there is a picture of a veiled woman and a 'WARNING' stamp. The other side has a letter addressed to "Fellow English resident" and sets out Jayda Fransen's reason for standing in the by-election.
Ms Fransen, deputy leader of Britain First, is contesting the seat because of the new mosque that is to be built in Railway Street, Gillingham.
On the Britain First website the group said Royal Mail's decision is "illegal" and based on "political reasons".
The post reads: "Royal Mail left-wing goons who have tried this kind of nonsense on before have been threatened with arrest for the same thing."
The Royal Mail has a legal obligation under the Representation of the People Act 1983 to deliver Parliamentary election mail but can refuse to carry it if they consider the contents to be illegal.
A Royal Mail spokesman said: "Royal Mail may refuse to carry election mail if we consider its contents to be illegal, for example if it is threatening, abusive or insulting or is intended to cause distress or anxiety.
"We have procedures in place to evaluate whether election mail complies with the law.
"In this instance, we consider that the election mail in question does not comply with the law and have therefore refused to carry it.”