Power Grid: Taxes card is shuffled into the power plant deck. If drawn in Step 1, place it below the power plant deck. If drawn in Step 2 or Step 3, all players must pay 20% of their money as taxes at the start of phase 5 "Bureaucracy", then remove the card from the game. After paying taxes, players receive their usual income for supplying electricity to cities.
For more information: http://boardgamegeek.com/boardgameexpansion/147932/power-grid-taxes