The IRS commissioner has said that the 2015 tax season "will be one of the most complicated" ever, according to the Journal of Accountancy. And whether you're a worker or a business owner, complicated could well turn out to be a euphemism for painful and demoralizing. For much of the pain, you can thank Washington, D.C. and its continued inability to come to a deal on immigration.

The interplay and fallout are a bit complicated. Let's start with the coming pain. The confusion mentioned by IRS Commissioner John Koskinen in a speech he gave in early November largely has to do with a few factors, including a lack of budget for enough staff to process returns and the implementation of individual mandates and tax credits in the Affordable Care Act. But that's not where the biggest pain for businesses resides.

For that, you have to look at the now-regular congressional approach to the tax code and provisions that periodically expire. There are a number of popular tax deductions, credits, and other considerations that are not permanently enacted. Instead, they become bargaining chips--more on that in just a moment. Unless passed, they go out of force and are unavailable, even though companies typically have to plan in advance to use them.

According to a conversation I had with Mark Luscombe, principal federal tax analyst for publisher and information-services provider Wolters Kluwer, the most popular provision is the R&D tax credit, in which companies can get an additional credit for certain types of research and development work. It's basically an extra deduction that becomes available for R&D spending, but only if it's reenacted.

But that's hardly all. If you run a business, chances are you're familiar with Section 179, which permits accelerated depreciation. Instead of treating the purchase of capital goods over time, to match their estimated lifetimes, you deduct the entire thing at once. It makes the process much easier and gives you a much bigger advantage in the year of purchase. Section 179 has had a temporary $500,000 limit, but that now heads back to a maximum of $25,000.

"Because it's a cry wolf situation, a lot of people assume [the provisions] will be enacted and proceed as if they will," Luscombe says. "But there's always the risk that it won't. The House would prefer to make some of these permanent and make a temporary extension of the rest. The Senate would prefer to make all of them temporary." Given the divisive atmosphere in Washington and the certainty of a Republican-controlled Congress at odds with Obama, the chance of non-renewal is significant.

All that brings us to the conflict between a tax deal and immigration, according to Politico.

The Senate and House had tax panels working on reenactment of the now-expired tax provisions. And then the deal fell apart.

The immigration executive order soured the GOP on the tax cuts for the working poor and middle class sought by Democrats. Republicans worried undocumented immigrants targeted by the order would begin claiming the credits in droves. They found a friend in Senate Majority Leader Harry Reid, who reluctantly agreed to drop his party's demands to extend expiring parts of the earned income tax credit and its companion, the child tax credit.

That means the IRS still doesn't know what the final tax landscape will look like, although it could make a decent guess. Without absolute knowledge, it can't provide up-to-date forms, can't tell tax professionals and software companies exactly what they will have to do, and can't even make the necessary modifications to their own software to process returns. It is going to be a mess, and unless Congress and the president miraculously get their collective act together, it will also cost a lot of entrepreneurs extra money.

Separately, in the when-it-rains-it-pours department, there are the major changes in which expenditures companies should capitalize and which they can treat as expenses. Many companies of all sizes will have to change their accounting methods to accommodate the rule changes. "Almost any business with depreciable assets" will have to file additional forms to document their accounting changes, according to Luscombe.

It should be one interesting tax season, indeed.