Last year, owners of small businesses had to cope with higher tax rates. This year, they will wrestle with greater uncertainty about the fate of some deductions they have come to rely on.

Congress has not renewed the so-called extenders, about four dozen provisions in the Internal Revenue Code that permit write-offs of various types of business expenditures and expire periodically, most recently at the end of 2013.  Most or all of them could be reinstated, although no vote has been scheduled. Unless and until they are, tax specialists warn, it will be hard for business owners to make informed decisions about spending for capital equipment, research and development, and even new employees.

"The extenders didn't get extended," said Kate Barton, vice chairwoman for tax services at the Americas tax practice of Ernst & Young. "Every company in the United States right now has to plan for 2014 without the research credit, the Work Opportunity Tax Credit and a whole bunch of other provisions. It's a real bummer for small companies."

The first credit is for part of expenditures on qualified research and development. The second is for a part of the wages of new employees drawn from certain segments of society, including military veterans, welfare recipients and ex-felons.