Jeffrey Bart, the third-generation owner of Granite State Candy Shoppe in Concord, N.H., has never collected sales taxes. That is probably about to change.

New Hampshire is one of five states without a broad-based statewide sales tax, a status that had insulated Mr. Bart and other retailers from a task familiar to businesses elsewhere. That cushion lasted until the U.S. Supreme Court’s June decision in South Dakota v. Wayfair, which lets states require retailers to collect sales taxes even if those businesses lack a physical presence in the state.

That decision was a “huge mistake,” says New Hampshire Gov. Chris Sununu, who expects to sign legislation this week to make it harder for other states to impose collection requirements on New Hampshire retailers.

“We’re not saying states can’t do it. We’re just putting up a lot of hurdles that states have to jump over,” Mr. Sununu said. “We’re not going down without a fight.”

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New Hampshire’s attempts to restrain fellow states’ collection efforts will have trouble succeeding because the Constitution’s “full faith and credit” clause requires states to respect one another’s legal judgments, said Daniel Hemel, a professor at University of Chicago Law School specializing in taxation.

“Our Constitution doesn’t allow states to wall themselves off from the operation of other states’ laws,” he said. “Maybe Chris Sununu would get some political points from the small business community in New Hampshire, but it doesn’t seem to me like a serious endeavor.”

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