How does this work?
If a card says to reduce a production that is already at zero, does that mean you can't play the card (as it's part of the cost) or does it mean you can ignore that effect (i.e. reducing production) on the card?
Megacredit production is the only production that can go negative.
For any of the other productions, you cannot play a card that would require you to go negative.
This is probably why one of the basic actions is to increase your energy production. Many cards require you to decrease energy production and it would be terrible if you were completely reliant of cards to increase energy production.