Sometimes alliances are formed between forces that, whilst not openly hostile to one another, could hardly be described as firm friends. Neither party has any reason not to trust the other – they just can't quite bring themselves to do so.
An allied contingent that is noted as being Uneasy follows all the normal rules for an allied contingent. In addition:
All units belonging to an Uneasy allied contingent are considered to have the Levies special rule by all units belonging to the main army.
Units belonging to an Uneasy allied contingent are not considered to be 'friendly' by Wizards belonging to the main army for the purposes of spell targeting, and vice versa.