By Jonathan Stempel

NEW YORK, June 25 (Reuters) - Piper Sandler PIPR.N and Stifel Financial SF.N on Wednesday asked a judge to free them from "onerous" restrictions from the U.S. Securities and Exchange Commission's global settlement more than two decades ago with 12 investment banks over analyst conflicts.

The $1.5 billion settlement in 2003 and 2004 addressed a scandal over analysts issuing positive research to help Citigroup C.N, Goldman Sachs GS.N, JPMorgan Chase JPM.N, Morgan Stanley MS.N, the defunct Bear Stearns and Lehman Brothers, and others win investment banking business.

In a filing in Manhattan federal court, Piper and Stifel said they should not be bound to requirements in a related consent decree, including having to build "firewalls" between research and investment banking, while nearly all rivals are held to looser standards the SEC approved in 2015.

Piper and Stifel said the disparate treatment makes it harder to compete with other middle-market banks, as well as large banks that are bound by the settlement but have much larger client bases and are better known globally.

They also said the decree hurts the public interest because research may have different protections depending on which bank issued it, and smaller companies may struggle to raise capital because compliance costs mean some banks cannot afford to provide research coverage.

"The consent decree has achieved its purpose," Piper and Stifel said.

An SEC spokesperson declined to comment.

Piper is based in Minneapolis, and Stifel is based in St. Louis. They are the respective successors to US Bancorp Piper Jaffray and Thomas Weisel Partners, the smallest investment banks in the SEC settlement.

The settlement had been engineered mainly by former New York Attorney General Eliot Spitzer, addressing alleged conflicts by analysts like Citigroup's Jack Grubman and Merrill Lynch's Henry Blodget.

The cases are SEC v US Bancorp Piper Jaffray Inc, U.S. District Court, Southern District of New York, No. 03-02942; and SEC v Thomas Weisel Partners LLC in the same court, No. 04-06910.

(Reporting by Jonathan Stempel in New York; Editing by Chris Reese)

((jon.stempel@thomsonreuters.com; +1 646 223 6317; Reuters Messaging: jon.stempel.thomsonreuters.com@reuters.net))