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They will if the merchant wants to. Otherwise I don't see how. How would you tax something that everyone can plausibly deny having received?
Unless they disclose their merchants BitCoin address, so the IRS can monitor and tax it, there is no feasible way.
But then again, if you are a merchant, they may force you to only accept payments to this particular address. You never know who your customer is.

In the US they have already set sort of a guideline....you just have to move the crypto to USD first.