The letter, from an organisation styling itself as Ulster Awakes, criticises Muslims and other groups.
Alliance Deputy Mayor of Lisburn and Castlereagh Stephen Martin said that the leaflets were left on car windscreens outside Bow Street Mall in Lisburn on Saturday afternoon.
It follows a similar incident in East Antrim several months ago.
“Everyone is entitled to express their point of view but when a group pretends to defend us all by spreading outright lies intended to divide communities, it needs condemned in the strongest possible terms,” said Alderman Martin.
“This propaganda needs continually challenged – nothing of what they have put into the public domain that actually stands up to scrutiny. These sorts of groups are only interested in whipping up unnecessary fear to further their own agenda.
“Whoever wrote this offensive material won’t even put their own names to their propaganda. These anonymous cowards need challenged on their lies at every turn.”