Since WI has conformed its laws to the SSTP, then it should be admitted as a full member of the Agreement. Once that happens, then amnesty will be available for a one year period. The SSTP amnesty is pretty great because companies are not only forgiven penalty and interest but the tax also. However, the downside is significant. You also have to register with all SSTP states and those in the Agreement for over a year offer no amnesty at all.
Here's the details according to CCH: Wisconsin Gov. Jim Doyle has signed a budget repair and economic stimulus bill that enacts provisions conforming Wisconsin sales and use tax laws to the Streamlined Sales and Use Tax (SST) Agreement.
Wisconsin sales and use tax laws are conformed to the SST Agreement, effective October 1, 2009. With the enactment of this legislation, the state may petition to become a full member of the Agreement. The state must be found in compliance with the Agreement by the SST Governing Board before it can become a full member of the Agreement.
Amnesty: A seller is not liable for uncollected and unpaid state and local sales and use taxes, penalties, and interest on previous sales made to Wisconsin purchasers if the seller registers with the Department of Revenue to collect and remit taxes on such sales in accordance with the SST Agreement. In order to receive amnesty, the seller must:
-- register within one year of the effective date of the state's participation in the Agreement; and
-- collect and remit state and local taxes on sales to purchasers in Wisconsin for at least three consecutive years after the date the seller registers.
Amnesty is not available to sellers that were already registered with the Department during the year immediately preceding the effective date of Wisconsin's participation in the Agreement; sellers that are being audited by the Department; or sellers that have committed or been involved in fraud or an intentional misrepresentation of a material fact.