(Bloomberg) -- A Bill Ackman SPAC told a judge that proposed rules for the vehicles support its defense against a lawsuit alleging it is acting illegally as an investment company.

In a letter to the court on Monday, lawyers for Ackman’s Pershing Square Tontine Holdings Ltd. said the recent plan by the Securities and Exchange Commission “does not state that all SPACs are -- or any existing SPAC is -- an investment company” as defined under U.S. securities law. 

Special purpose acquisition companies, or SPACs, are shells designed to buy another company with the investment money they attract. Pershing Square Tontine is the first of a number of such blank check companies, as they are also called, targeted in suits by a group of lawyers led by former SEC commissioner Robert Jackson and Yale Law School professor John Morley. 

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The lawsuits claim the companies violate the Investment Company Act of 1940, which requires them to register with the SEC and places limits on fees that can be charged for investment advice. The litigation could have broad implications for the financial industry if a court determines that SPACs in general should be regarded as investment companies subject to the law.

The SEC’s new rules, proposed on March 30, would require SPACs to disclose more information about their sponsors and potential conflicts of interest. 

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“Indeed, if anything, the proposed rule underscores yet again -- as defendants have argued all along -- that the SEC, not an opportunistic private litigant, is the statutory gatekeeper with the regulatory authority and responsibility for assessing whether a SPAC is an investment company,” attorneys for Pershing Square Tontine told U.S. District Judge Analisa Torres in the letter Monday. 

The SPAC has said the SEC has approved more than 1,000 blank check companies since 2003 without requiring any of them to register under the 1940 law and that Tontine’s only purpose is to effect a business combination. 

Another SPAC sued by the Jackson group, Go Acquisition Corp., co-founded by Noam Gottesman, made a filing last month arguing that the new rules support its legal defenses.

Read More: SPAC Seizes On SEC’s Proposed Rules to Fight Investor Suit

Jackson had no immediate comment on Monday’s filing.

Only 56 SPACs have gone public in the U.S. so far this year, raising $10.1 billion, about a tenth of the total in the same period last year, according to data compiled by Bloomberg. Enthusiasm for blank check companies has waned as some of the mergers have delivered lackluster stock market performance and others have seen increased regulatory scrutiny.

After voting to propose the regulations, the SEC began taking public comment on the plan for as long as 60 days before making changes and holding a second vote to finalize the rules.

The case is Assad v. Pershing Square Tontine Holdings, 21-cv-06907, U.S. District Court, Southern District of New York (Manhattan). 

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