Tax Sweeper is a uncommon Sorcery card from Unknown Event (UNK), collector number UU14b. Current market price: $25.00, TCGplayer market prices via Scryfall.
Creatures get -X/-X until end of turn, where X is your highest commander tax among your commanders. (For example, if you've cast your one commander from your command zone twice, creatures get -4/-4 until end of turn.)