Info:Upkeep

From DoW2.Info

Upkeep

Upkeep is a requisition tax that you pay to maintain your army. Each race starts with 0 upkeep, and it will remain 0 as long as you do not go over the population threshold of 30, and every unit after that will decrease your overall requisition income by a certain amount. Upkeep does not affect power.

For example: The upkeep of a single Guardsman is 2.55, if you have 5 squads of unupgraded Guardsmen, you will reach a total of 30 with no upkeep penalty. At this point if you build the 6th Guardsmen squads you will suffer a 15.3 requisition income penalty for the extra 6 men you have over 30. (2.55x6=15.3).

Only the most expensive units are taxed this way, you can build the most elite units first which usually have the highest upkeep, but once you are over 30, they will be the first to be penalized.