Tax law is dependent on your country and locality. Recently in the United States, the IRS has declared that Bitcoin is to be treated as property, not currency, for tax purposes. All income in the US is taxed, regardless of what form it takes. If youre paid in bitcoins, youre supposed to pay taxes on your earnings at the BTC/USD exchange rate when you receive payment.
Is it a good decision or bad?
I do not agree if BTC usage is taxed.
If they use BTC, but they don't have BTC in their wallet, do they have to pay taxes?
I think the government is enough to receive building taxes, vehicles.