Not to mention the cost to handle - collect, store, archive, query, and ultimately act upon - the data would be higher than the funds raised.
And how would this raise funds? It doesn't. In our credit-heavy society there's nothing at all that ties a persons income to their spending levels (or, seemingly, to the amount of credit they can get approved for) so there's no valid way to infer higher income than reported based on credit expenditures.
If this passes I'll stop using my credit & debit cards. Maybe I'll use rolls of nickels when it comes time to buy that HDTV or new car. I would think the implications of lost business for etailers and increased processing costs for not only merchants but card processors and issuing banks would cause them to lobby against it.
Furthermore, how is this not a violation of privacy? Granted, the right to privacy is mostly implied and not specifically declared in the fourth amendment, but the judicial branch has interpreted the language to mean we've a right to privacy. Right now if I use a credit card to buy something online, only me, the merchant, and the payment card companies have any knowledge of the transaction. This is not publicly observable data; it is private by nature. It matters not if I'm purchasing porn or iPods; there's nothing about the transaction that the government has any reasonable right to know about.