Unite Against Fascism (UAF) has called upon supporters to stand against a Britain First march on Saturday.
Britain First supporters are set to meet at Charing Cross station for a march against terrorism on April 1 at 1pm, in light of the terror attack on Westminster last week.
Their Facebook event says: "Enough is enough! Join us to protest against radical Islamic terrorism!"
However, UAF has said the march is in "haste to incite Islamophobia and hatred of Muslims."
It also claims that the English Defence League will be joining the march.
UAF claim "both groups are notorious Islamophobes whose concern is not with the victims or their relatives, but only lie in racism."
UAF has asked anti-fascists to meet on April 1 at 12pm, ahead of the march, at South Africa House to oppose the groups.