With the Internet tax moratorium set to expire, Congress is considering measures that would expand existing sales taxes. This would limit state competition, hinder the Internet’s ability to hold government accountable, and harm taxpayers. For these reasons, legislators should ignore their self-interest and renew the moratorium, no strings attached.

The original law, which expires on October 21st, banned taxes that discriminate against the Internet, such as those on Net access. But, contrary to popular belief, sales taxes were not affected; each state retained its right to collect these taxes from online businesses. However, the Constitution and the Supreme Court limit this right.

The Constitution explicitly bars one state from regulating the commerce of another, which in this case means taxing retailers located across state lines. In the 1992 Quill decision, the Supreme Court affirmed this principle by ruling that a state can only collect sales tax from businesses that have a “nexus,” or substantial physical presence, in that state. For example, because Amazon.com is based in Washington state, buyers there are taxed on Amazon purchases. Consumers in Illinois, where Amazon has no physical operations, are tax-exempt. Some legislators, pressured by revenue-hungry state governors, are trying to erase this benefit.

Senators Byron L. Dorgan (D–ND) and Ron Wyden (D–OR), among others, want to burden a renewed moratorium with new provisions that would let states collect sales taxes from all retailers, regardless of their location. The prerequisite is that at least some states first streamline their tax codes, making it easier for online businesses to collect. States are embracing these proposals, and many—such as the 38 members of the Streamlined Sales Tax Project—are working to adopt a nearly uniform sales tax code. But, by expanding states’ authority against the wishes of the Framers and the Court, these laws would harm taxpayers now and in the long run.

Advocates cite two reasons for the tax expansion. First, they point out that bricks-and-mortar retailers have a disadvantage to online businesses selling tax-free goods. Second, they explain that e-commerce will slowly suffocate state governments by eating away at their sales tax revenue. But these arguments only justify expanded sales taxes if you elevate state governments' interests above taxpayers' interests.

Expanded sales taxes, which amount to a tax increase no one voted for, would pave the way for bloated governments while making it harder to hold them accountable. States would receive unprecedented new authority to tax and regulate out-of-state businesses. This would expand their revenue and power while partially neutralizing two checks against government growth: e-commerce and tax competition among states.

E-commerce allows consumers dissatisfied with local taxes to go online and find lower prices. This erodes local retailers' profits. Together, falling government revenues and suffering businesses signal state and local officials that taxes are poorly structured or too high. But this signal would be unimportant were it not for tax competition among states.

Today, dissatisfied businesses can relocate to states with more favorable tax codes. In high-tax states, this scenario is more likely because of the advantages favoring online businesses; traditional retailers are tempted to move where sales taxes are lower or don't exist.

If these mechanisms remain in place, states must adapt. Over time, sales taxes would likely be replaced with more efficient alternatives. But this would force state governments not only to change but also to abandon an opportunity to expand their authority and revenue. And this runs contrary to the survival instincts motivating today's politicians.

This is the real reason why governors are suddenly crying foul. With a choice between expanded power and enforced fiscal responsibility, they will always seek the former. And this is why our Senators must step in and renew the moratorium in only its purest form. Such a move would protect not only taxpayers and the Internet, but the sanctity of the Constitution itself.

Justin Matlick is a Senior Fellow for the Center for Freedom and Technology at the California-based Pacific Research Institute.