Yahoo Inc. is proceeding with the spinoff of its stake in Chinese e-commerce giant Alibaba even without guarantee that it won't be taxed.

In a regulatory filing, Yahoo says its board has authorized the transaction despite lacking an approval from the Internal Revenue Service. On news of the decision, Yahoo's shares rose Monday by as much as 4% in extended trading.

The company said the spinoff would still be subject to other conditions, including  receipt of a legal opinion outlining how the transaction would be tax-free under US federal tax laws.

This comes as Yahoo chief executive Marissa Mayer faces intense pressure from shareholders to spin off nearly 384 million shares in Alibaba. That's worth $22 billion or nearly as much as the value of Yahoo itself.

Yahoo's plan is to cede control of the Alibaba stake to independent public company, Aabaco Holdings, and distribute it among the stakeholders of the Web portal.

Earlier this month, Yahoo requested the IRS to rule on whether the spinoff would be tax-free. The request was denied, raising the possibility of Yahoo shareholders paying some $9 billion in taxes.

The IRS has said it was in the process of amending the rules on taxing such transactions. But some analysts say Yahoo may be able to spin off its Alibaba shares before the IRS comes up with new rules.

"In our opinion, the IRS is maintaining the status quo on this issue, and with no changes to guidance on this matter, we believe that Yahoo should be able to complete this transaction in a tax-free manner," Mizuho Securities analysts said in a note.

The transaction is expected to close in the fourth quarter.

Pressures for a spinoff come as Yahoo's shares in Alibaba lose nearly 50% in value this year. That's amid a slowing Chinese economy and tough competition from Alibaba rival, JD.com Inc.

Yahoo acquired a 40% stake in Alibaba 10 years ago for $1 billion.