Colorado has fought a hard battle to claim the state sales taxes that it argues online retailers such as Amazon should cough up.

After years of resisting, Amazon, the country’s largest online retailer, on Feb. 1 began collecting Colorado’s 2.9 percent state sales tax, a move that could pour millions into state coffers.

But absent a change in the state’s tax system — or another economic downturn — much of that money could go back out as tax refunds in the years ahead because of limits set by the Taxpayer’s Bill of Rights (TABOR).

“Assuming that we’re right, new sales taxes collected this fiscal year will not be refunded and will increase the amount of money available for the budget. However, any new taxes collected beginning next year will increase the amount required to be refunded to taxpayers,” said Natalie Mullis, chief economist for the Colorado Legislative Council.

Colorado will get to spend five months worth of what Amazon remits, before having to refund future collections, at least for the next two fiscal years, and possibly more.

State sales tax collections are subject to TABOR, which limits tax revenue increases year-to-year using a formula linked to population growth and inflation.

“There’s really no point in celebrating some windfall … when we have been pushed over the TABOR line by a fake surplus,” said Tim Hoover, spokesman for the Colorado Fiscal Institute, which wants an overhaul of the tax limitation measure voters added to the state constitution in 1992.

The online sales tax revenues Colorado fought so hard to get will have to be refunded, even as the state cuts spending on schools, colleges and roads, he said.

“That’s why TABOR is so bonkers,” Hoover said.

Under federal law, state and local governments can’t require retailers who don’t have a physical presence in their jurisdictions to collect sales taxes. With more retail sales moving online, revenue losses have become a bigger worry for local and state governments.

After the recession blew a big hole in the state budget, Colorado lawmakers passed a law requiring online retailers to track purchases by state residents, report those transactions and to advise customers of their obligation to pay the required taxes.

The Direct Marketing Association challenged the law in a case that went all the way up to the Supreme Court before getting kicked back down to the lower courts, which ruled in Colorado’s favor last month.

Amazon fought back hard, cutting ties to its Colorado retail partners in 2010, in part to remove any questions on whether it had a local presence.

It remains to be seen how much the retail giant will remit to the state, and how much of that will end up in the pockets of taxpayers. In 2014, the Colorado Department of Revenue estimated it was losing $172.7 million in potential tax revenue as sales migrated online.

“Amazon would be a significant share of that, but likely a small share,” said Michael Mazerov, a senior fellow at the Center on Budget and Policy Priorities in Washington, D.C.

Mazerov said he didn’t know of any other states facing Colorado’s predicament of having to turn around and refund new sources of online sales tax revenues.

Whether taxpayers get a refund is secondary to online retailers like Amazon charging and passing on what they are supposed to in retail taxes, argued Chris Howes, president of the Colorado Retail Council, which represents large chain retailers in the state.

“Hopefully, if that money comes back to the citizenry, they will spend it in their local stores,” he said.

Aldo Svaldi: 303-954-1410, asvaldi@denverpost.com or @aldosvaldi