Chinas e-commerce giant Alibaba Group Holding Ltd is planning a U.S. IPO in the third quarter of this year, people familiar with the matter told Reuters, in what is the expected to be a more than $15 billion deal. The Hangzhou, China-based company, which controls about 80 percent of the countrys e-commerce, had been in discussions with the Hong Kong stock exchange and the Securities and Futures Commission since last year about a potential listing, but the island citys regulators blocked its proposal as it violated the one-share-one-vote principle. After an initial rebuff, Alibaba and the Hong Kong regulators were back at the negotiating table late last year, to find a solution to the vexed problem. While the Hong Kong Exchanges and Clearing Ltd has initiated a review of its listing rules to accommodate more flexible structures, any change to the existing rules would take months.