Yahoo is reconsidering its plan to spin off its $23 billion stake in Alibaba after federal tax authorities declined to rule in advance on whether the transaction would mean huge capital gains taxes for Yahoo or its shareholders.

Yahoo disclosed in a securities filing on Tuesday that the Internal Revenue Service told the company on Sept. 2 that it would not provide any guidance about the tax liability related to the spinoff ahead of the deal.

The Internet company said that its own tax advisers still believed the spinoff of its 15 percent stake in Alibaba, a leading Chinese e-commerce company, would be tax-free, in part because it would be bundling a small-business division with the Alibaba stock into a new company called Aabaco Holdings.

However, Yahoo said its board was now considering its options in light of the I.R.S. decision.

Analysts say Yahoo’s options could include restructuring the spinoff or selling all or part of its 15 percent stake in Alibaba.