The act’s passage would put New York at the “vanguard” of a national movement, 15 state and national labor and policy groups wrote in a letter to legislators that DealBook is first to report. The organizations argue that the law would “rein in many abusive tactics corporations use against other firms and workers that are difficult to challenge under current antitrust law and precedent.”

Market dominance would be presumed with 40 percent market share. Currently, companies qualify as dominant if they have 70 to 90 percent of a market. “It’s not illegal to be dominant,” said Pat Garofalo of the American Economic Liberties Project, one of the groups that signed the letter. “It’s just illegal to block others from the market unfairly.” In the act, an “abuse of dominance” standard would replace the current “consumer welfare” standard.

• “Where New York goes, often the rest of the country follows,” Garofalo said, and lawmakers at the federal level could be motivated “if they see the ship is leaving port.”