One serious problem is the question of defining session boundaries of winning and losing. At the blackjack table every time you win a hand you have winnings. So if I am betting $100 per hand for 100 hands, win 40 hands and lose 60, have I lost $2000 or won $4000 according to this law?
Or suppose I am staying at a casino resort for 2 days, win $5000 on Saturday and lose $6000 on Sunday. Have I lost $1000 or won $5000? When you leave Las Vegas with less money than you came in with no one would consider that "winning", but as this law is written it would appear they think a person who wins money at Bally's and gives it all back at Paris later that day has winnings.
Such a law would put a gambler is the horrible situation of having a winning session, followed by a much worse losing session, and having to remain at the table hoping for another big win so he will have enough money to pay his taxes. If he loses it all, he will be both bankrupt and liable for the taxes on all the money he "won." This is a law that needs to be challenged.