Sen. Rand Paul could prove to be an obstacle in Republican leadership's preferred path for tax reform.

The senator criticized the legislative approach suggested by his fellow Kentucky Republican and Senate Majority Leader Mitch McConnell on Wednesday, writing in an op-ed that the idea of pursuing an overhaul of the tax code that does not lower revenue is "a terrible idea."

"Tax reform can be simple, but I'm afraid those who are in charge will make it unnecessarily complicated," Paul wrote in an op-ed for CNN.

Paul said he fears that a bill that aims not to lose revenue would mean that tax cuts for some would have to result in tax increases for others.

Instead, he argued, Republicans should simply cut taxes. He called for cutting taxes for all individual taxpayers and for lowering the corporate tax rate to 15 percent.

Last week, McConnell said at an event in Louisville, Ky., that the likely legislative approach for tax reform would be a permanent rewrite of the tax code that is revenue-neutral, meaning that it raises as much revenue as the current system.

"I think that's where we're likely to end up," McConnell said, while acknowledging that Republicans are still debating the matter.

Pursuing a tax code overhaul that does not add to long-term deficits would allow McConnell to pass legislation using the procedural tool known as budget reconciliation. Reconciliation allows a bill to pass with only 51 votes in the Senate, bypassing a potential Democratic filibuster.

To use that tool, however, the Senate first would have to pass a budget. Paul's vote might be needed to do that.

And any "revenue-neutral" tax reform backed by McConnell would likely be revenue-neutral only on paper. In reality, Republicans are likely to advance a net tax cut.

That's because, since taking over the Senate, congressional Republicans have implementing "dynamic scoring" of tax bills, which estimates how much revenue is created through business growth and job growth resulting from tax cuts.

So a bill that is revenue-neutral in a dynamic score on paper might actually be a net tax cut, but one that partially pays for itself through faster economic growth.