Occaisonally, a lord will find himself strapped for cash and will need to raise additional funds to proscute some enterprise - and to do so, he imposes a feudal levy on his populace, a special tax to raise coin.
This levy raises money immediately, but at a cost of popularity and loyalty for potentially the next year. The amount raised is based on the size of a fief and is expressed as percentage decrease in annual income.
For fiefs with more than approximate 15,000 people, the amount raised in income for every 1% of annual feudal levy is 0.3% of the fief's total population. This decreases the lord's income, loyalty, and popularity for 1% for the duration of the levy. Like conscription (on which the feudal levy is based) subinfeudinated lords also suffer the full income penalty and 'trickle-down' loyalty and popularity penalties.
Below 15,000 people the economy of scale for a feudal levy diminishes, and every 1% of feudal levy (with its associated penalties) merely increases fief income by 1.5%. The graduated nature of the income scale means that fiefs below 15,000 operate on very different equations than fiefs above 15,000, requiring a separate method to figure smaller fiefs. In general, feudal levies benefit large landholders more than small landholders ICly and a consequently a source of great discontent between lesser lords and their betters.