Yahoo Inc (YHOO.O) shares fell 7.6 percent on Tuesday on concerns that a possible change in U.S. tax regulations would affect Yahoo’s planned spinoff of its stake in Alibaba Group Holding Ltd (BABA.N). The change – discussed by a U.S. Internal Revenue Service (IRS) official in Washington – could complicate the plan announced by Yahoo in January to spin off its 15 percent stake in Alibaba tax free. Yahoo said in a statement that it understood the IRS statement was not specific to Yahoo’s planned spin-off of its remaining stake in Alibaba Group and its Small Business unit.