WSB has reported that a group named The Atlanta Tea Patriots will file a lawsuit within 10 days in an effort to block the tax payer funding of the new stadium. It's difficult to say very much about how much merit the suit will have, since we know none of the details. However, the tea partiers used the language "unconstitutional" which would seemingly indicate it's not just a procedural issue that they're questioning, as Craig Calcaterra supposed.
If it is just a procedural issue, it shouldn't raise any problems. However, based on the language used by the group, it would seem that they're challenging the Commission's right to extend a tax that was set to end for an additional 30 years without a referendum.
In Cobb County, the creation of new taxes typically requires a voter referendum by law. The Commission could not simply decide they wanted to raise property taxes to fund the new stadium. The key to the Cobb plan, however, was that a park tax, that was set to expire in 2014, could be extended without a voter referendum. Taxes can typically be extended without requiring a voter referendum. Further, budgetary dollars can also be reallocated without a referendum. What the Tea Party group seems to be implying however, is that doing both of these simultaneously amounts to creating a new tax, which would require a voter referendum.
There's some "spirit of the law" validity here. Extensions of taxes typically don't require voter referendum for cases where a project runs into delays, so that changing politics wouldn't leave a project half finished. Envision a highway project that ran a year longer than expected: while that might be irksome to taxpayers, it would just be purely wasteful if it got 90% finished, but then a vote against the extension caused the 90% of it that was done to simply lay fallow.
Allowing commissioners to reallocate budgetary dollars is also a key component to letting a government operate efficiently, as occasionally costs for one project might grow, while the costs for another project aren't quite as high as originally envisioned.
However, neither of these abilities were really envisioned so that the commissioners could undertake a major new project, that would require 30 years worth of relatively substantial property taxes (as far as property tax hikes go) without a voter referendum. In effect the Commission is creating a new tax. They're creating a new expense for a very long time that is being paid for by tax dollars that were not originally envisioned for that project. This isn't shifting dollars around for existing projects in the way that reallocation is typically used.
Voter referendums are mandated to precisely avoid politicians spending money in this way, i.e. using public money to build a baseball complex for a private enterprise. I think it is fairly difficult to argue that the taxpayers of Cobb County "shouldn't" be able to vote on this project and the accompanying tax hike, in a civic right sort of sense.
However, there are likely two problems here:
First, as best as I can tell, while the actions of the committee may be in contravention of the spirit of the law, they seem to be well within the letter of the law. So far as I can tell there isn't a single provision saying they can't combine the two rights of using public funds the way they did. They can extend taxes, and they can reallocate budgetary dollars, and nothing says they can't do it simultaneously.
Secondly, there really isn't very much political opposition to the new stadium. Cobb residents seem to be overwhelmingly in favor of the stadium, and a voter referendum would likely just confirm that. If it were the case that a voter referendum would be likely to shoot down funding, we might be looking at a different picture. Judges seem much more amenable to "spirit of the law" sorts of arguments when they feel the public is being bamboozled.
It would be a difficult case for the Atlanta Tea Party Patriots to win if either of these two things were the case. The fact that they are both true indicates it's almost certain to ultimately go nowhere, and really just be a nuisance more than anything else to the Atlanta Braves.