When your gas tax went up in 2016, your sales tax went down.

And state lawmakers vowed that if New Jersey's sales tax was raised again, that 23-cent gas tax increase should go away. It was part of an effort to make sure the tax cuts enacted to balance out the controversial gas tax hike would actually last.

But now Gov. Phil Murphy wants to hike the sales tax back up to 7 percent. So will that mean you'd pay less at the pump? Don't hold your breath.

First, the governor will have to convince fellow Democrats who control the state Legislature to actually go along with his tax plans. State Senate President Stephen Sweeney, D-Gloucester, says tax increases are a last resort.

And if they do agree to raise the 6.625 percent sales tax to 7 percent, he'd have to find a way to overcome the taxpayer safeguard put into that gas tax law.

The gas tax was raised to replenish the flat-broke fund to pay for road and rail projects two years ago. But then-Gov. Chris Christie, a Republican, insisted that tax cuts be a part of the deal.

In addition to the sales tax, there were cuts to the estate tax as well as provisions to exclude more retirees from state income taxes and boost the Earned Income Tax Credit for the working poor.

The law also included this proviso: Alter any of these bonuses for taxpayers, and the gas tax increase goes away. In Trenton, that's called a poison pill.

"We wanted to have credibility that we're really serious about this," said state Sen. Steve Oroho, R-Sussex, who helped negotiate the gas tax hike.

But those assurances aren't air-tight and Sweeney and others don't think it would be much of an obstacle to raise the sales tax without cutting the gas tax.

The law says a three-person council would have to vote to trigger the poison pill provision if the sales tax hike made it into law. It would be comprised of the state treasurer, the head of the nonpartisan Office of Legislative Services' budget and finance office and a third person they mutually appoint.

Frank Haines, budget and finance director for OLS, said in a public hearing Tuesday that a third member has not been appointed. But he made it clear he would stick to the law enacted two years ago.

"If we get to the point where there is a law signed that reverses the sales tax and doesn't change any other part of the law, I know how I would have to vote," Haines said. "And I would have to vote based on the fact that the steps have been reversed."

But without a third member, it could be expected that Haines and the state treasurer, a Murphy appointee, would tie and take no action.

It may not come to that, however. If Democrats do eventually get on board with Murphy's tax hikes, the Legislature could attempt to neutralize the poison pill through language inserted into the state budget. Or lawmakers could pass a separate bill to ensure the gas tax stays where it is.

State Sen. Declan O'Scanlon, an assemblyman at the time the gas tax deal was struck, said Democrats will be risking a lot if they go along with Murphy.

"I think it's a hell of a credibility killer for anyone who voted on the original package ... just last session, and now you're going to vote to reinstate the tax," O'Scanlon, R-Monmouth, said. "If they're gonna destroy their own credibility here, how are you going to believe anything they say?"

The governor's office declined to comment. But a source in the administration, who ask for anonymity because they're not authorized to speak publicly about the budget process, said they are aware of the provision in the gas tax law, and that it will be addressed as a part of the governor's budget proposal.

Democrats weren't thrilled with the sales tax cut at the time, saying it would be a bigger hit to the state's budget than it would be a boon to taxpayers' wallets.

Murphy made that same argument in introducing the tax increase last month.

"Let's be honest, the impact of the three-eighths of one percent sales tax decrease has been nearly imperceptible to the average family," he said in his budget address, "but has directly impacted our ability to provide better services to, and greater investment in, that family."

The Office of Legislative Services estimated at the time the reduction from 7 cents on the dollar to 6.625 cents would cost state coffers $655 million a year by 2022.

Meanwhile, a household with income below $25,000 is expected to save $32 a year. It's a savings of $86 for a household with $49,000 to $79,000 in income and $116 for a household with $79,000 to $132,000 in income.

The sales tax is part of more than $1.5 billion in new taxes Murphy is proposing in his budget for the fiscal year that begins in July. He also wants to raise taxes on income over $1 million, tax ride sharing and home sharing and close tax loopholes on businesses and bonuses for hedge fund managers.