Bill Ackman’s blank-check company increased the size of its initial public offering, aiming to raise US$4 billion for an unspecified acquisition.

Pershing Square Tontine Holdings Ltd. is now marketing 200 million units for US$20 apiece, according to a regulatory filing Monday.

The special purpose acquisition company, or SPAC, had earlier marketed 150 million units for the same price, aiming to raise US$3 billion. The units include one share and a warrant for one-ninth of a share, plus a warrant that comes with special restrictions. Ackman’s Pershing Square Capital Management will at some point add to that pot with its own multi-billion dollar contribution, to help the SPAC acquire a target.

An earlier SPAC backed by Pershing Square, Justice Holdings Ltd., raised US$1.44 billion in a 2011 listing in London. That blank-check company merged with Burger King Worldwide Inc. in 2012 and brought the fast-food chain back to the public market, later merging with Tim Hortons Inc. and creating Restaurant Brands International Inc. Pershing Square remains the largest shareholder of Restaurant Brands, according to data compiled by Bloomberg.

Ackman’s new SPAC hasn’t specified which sectors it will focus on. However, the company’s filings have singled out “mature unicorns” -- or large, venture-backed businesses with significant market share and cash flow -- as of particular interest.

It also said it would be targeting large IPO candidates, private equity-backed companies in need of capital, private companies worth more than US$10 billion and family-owned businesses.

The SPAC could eventually raise as much as US$7 billion, including contributions of between US$1 billion to US$3 billion from funds associated with Pershing Square. Previously, it had been seeking to raise as much a US$6.45 billion, including a greenshoe for the underwriters, which has since been removed, according to the filing.