SAN FRANCISCO, United States — Yahoo! Inc. said it's on track to spin off its stake in Alibaba Group Holding Ltd. in the last three months of the year, a plan that the Web company has been pursuing to return shares in the Chinese e-commerce company to shareholders without incurring a multibillion-dollar tax bill.

Yahoo’s board authorized the spinoff, even though the U.S. Internal Revenue Service declined to grant the company an advance ruling blessing the deal, it said in a securities filing Monday. While the agency is stepping up scrutiny of such transactions, Yahoo is still going forward with the plan, which was announced earlier this year.

Chief Executive Officer Marissa Mayer is planning to spin off Yahoo’s 15 percent stake in China-based Alibaba, potentially saving about $9 billion. There’s been growing concern since May that Mayer won’t be able to complete the proposal.

“Neither this ongoing guidance project nor the IRS’s decision not to rule with respect to the Aabaco spinoff transaction changes the current law applicable to the proposed spinoff,” Yahoo said in a filing, referring to the corporate entity that will be spun off.

Yahoo also noted that an IRS official indicated this month “that any future guidance issued as part of the project would not apply retroactively to transactions completed prior to the issuance of such guidance.”

By Brian Womack; editors: Jillian Ward and Reed Stevenson.