The amended complaint filed on Tuesday in a federal court in New York adds a trade group that represents more than 200 restaurants and nearly 25,000 employees as plaintiffs.
The new complaint by Citizens for Responsibility and Ethics in Washington (CREW) is an effort to address concern over the lack of a clear victim or whether the watchdog itself was harmed by Trump businesses.
It said members of Restaurant Opportunities Centers (ROC) have improperly lost business, wages and tips to the president’s competing businesses.
Trump, who had argued that the original lawsuit had no merit, is expected to respond by April 21.
The lawsuit alleges that Trump violates the Constitution's "emoluments" clause, which bars him from accepting gifts from foreign governments without congressional approval.
CREW has warned that foreign diplomats could rent out space in Trump hotels in order to curry favor with the president or rub shoulders with his adult children who are in charge of his business transactions.
Trump’s lawyers argue that the emolument clause only prohibits federal officials from accepting a special consideration or gift from a foreign government and does not apply to payments such as a bill for a hotel room.
At the center of the controversy is the Trump International Hotel in Washington, which sits on federal property that Trump has leased from the General Services Administration (GSA) for 60 years.
The 2003 paperwork explicitly forbids any elected official from holding the lease or benefiting from it.
Trump does business with countries like China, India, Indonesia and the Philippines, and that is a cause for concern in future US trade deals with those countries.