You haven't heard much about Enhanced Section 179 expensing on the campaign trail. There's no mention of it in President Obama's 2013 budget or Romney's economic plan. But it's among the reasons that businesses are so worried about the looming fiscal contraction at the end of the year.

Most discussions of the fiscal cliff have focused on the automatic sequester spending cuts and the tax hikes that are set to take effect after Dec. 31. But there's a host of other tax breaks that are scheduled to end at the same time, which the Tax Policy Center's Donald Marron calculates will constitute about one-eighth, or $65 billion, of the cliff's impact. CBiz, a business services firm, has rounded up a few of the so-called extenders that will most directly affect the business community. (Some of them have already expired in 2011, but their full impact won't be felt until companies file their 2012 taxes next year.)

  • The research and experimentation tax credit (expired in 2011);
  • Bonus depreciation (100 percent bonus expired in 2011; 50 percent bonus expires in 2012);
  • Enhanced Section 179 expensing election (dropped from $500,000 in 2011 to $139,000 in 2012 and scheduled to revert to $25,000 in 2013); and
  • 15-year recovery period for qualified leasehold, restaurant and retail improvement property (expired in 2011).

There has long been a broad bipartisan consensus in favor most of the tax breaks on this list: The research and experimentation credit was originally passed in 1981 and has been extended 14 times since then to help boost R&D spending by businesses. The depreciation and expensing provisions were passed in 2002 then expanded during the recession to help encourage businesses to make more capital investments and allow them to write off more of the cost, increasing their cash flow.

But sorting through the dozens of so-called tax extenders adds yet another political and policy complication to the fiscal cliff debate. There's a lot of debate about the usefulness of the dozens of provisions at stake, which range from clean energy and charitable contributions to a so-called NASCAR loophole for accelerated depreciation of racetracks. The Congressional Research Service, for instance, points to various studies concluding that accelerated depreciation "is a relatively ineffective tool for stimulating the economy," with lower take-up than expected. Romney and other Republicans don't like the wind energy credit. And there are some from both parties who view the NASCAR loophole as a pork-laden giveaway.

Anticipating this complication, the Senate has put together a stopgap $205 billion tax extender bill. But despite bipartisan support, it stalled in the Senate last month. And it's just one more reason why getting around the fiscal cliff is going to be such a headache.