The NYSE announces that Bill Ackman's Pershing Square closed-end fund IPO has been postponed.

The highly scrutinized listing of Pershing Square's U.S. closed-end fund, which was to be done by billionaire investor Bill Ackman, has been postponed, according to a notice on the New York Stock Exchange's website.

The initial public offering of Pershing Square USA Ltd, with the ticker PSUS, has been delayed until a date to be announced, according to the website. Billionaire Ackman is now looking to raise $2.5 billion to $4 billion for the fund, well short of the $25 billion target from a few weeks ago, according to a regulatory filing dated Thursday.

Pershing Square declined to comment further.

Closed-end funds issue a fixed number of shares during their initial public offering (IPO) and then trade on stock exchanges after their launch. The fund's price may differ from the net asset value of its shares, resulting in a premium or discount.

"Ackman stated in a July 24 letter to investors that was included in the filing that there is enormous sensitivity to the size of the transaction. He emphasized that this is particularly true given the novelty of the structure and the negative trading history of closed-end funds. Ackman explained that it requires a significant leap of faith and careful analysis and judgment for investors to recognize that this closed-end company will trade at a premium after the IPO when very few in history have done so."

At the end of June, Pershing Square had $18.7 billion in assets under management, with most of its capital invested in Pershing Square Holdings, a $15 billion closed-end fund that trades in Europe. Ackman is looking to launch a similar closed-end fund listed on the New York Stock Exchange, which could potentially lead to an IPO of his management company.

Ackman's public listing of his fund is viewed as a strategy to capitalize on his growing influence among Main Street investors, who follow him on social media platform X, where he discusses a range of topics including antisemitism and the presidential election. The publicly traded closed-end fund is expected to invest in 12 to 24 large-cap, investment-grade, "durable growth" companies in North America.

In his roadshow presentation, Ackman emphasized the difficulty of managing traditional hedge funds due to the potential for investors to withdraw their funds at any time, which requires continuous fundraising and investor soothing. However, managing permanent capital allows him to concentrate on the portfolio and adopt a long-term investment strategy.

The challenge of managing a portfolio where money can come and go is significant for long-term investors, as action can have a significant negative impact on one's returns, according to Ackman.

— CNBC's Leslie Picker contributed reporting.