Your leading political party is the industrialists. Their forced law gives you dust when you build improvements.

 Any resources gained from completing constructions are given to your empire separately at the end of turn and the amount doesn't show up in your income.

@Touko, ok, it makes sense, thanks, however, it would be clearer to players if the calculation for the next turn in the upper left corner was taking this amount from the law (and all other factors) into consideration, and showing the correct, complete actuals of the next turn, so that there are no surprises from that end :)

It's not a direct increment to your Dust during turn processing, so I guess suprises might happen even if you somehow code it in there. For example, law, that increases Industry might be cancelled, population, that contributes to Industry output might starve out, and building won't be finished on that turn. Even upon elections or anarchy, that basic law might get cancelled, so you won't get your Dust.