Billionaire investor Carl Icahn is building a "significant" stake in U.S. discount store operator Dollar Tree Inc., the New York Post reported Oct. 16, citing sources.

Icahn's plans for the stake are reportedly still unclear, but insiders suggest that the investor could push the company to reverse its $8.5 billion acquisition of Family Dollar Inc. in 2015 by proposing a sale or spinoff of the discount retailer, the newspaper said.

Family Dollar could be valued at $5 billion to $6.2 billion if spun off, according to the Post.

Shares of Dollar Tree spiked around noon on Oct. 16 following the report and ended the day up 6.83%.

The newspaper said Icahn declined to comment on the matter.