By Laura Jarrett CNN

(CNN) -- A local DC restaurant is taking President Donald Trump and his luxury hotel in Washington to court in the first lawsuit alleging unfair business competition since Inauguration Day.

The lawsuit was filed in DC superior court by a married couple that owns the Cork restaurant, located 1.5 miles from the Trump hotel. They said they can't compete with the President because he has a "big leg up" with foreign dignitaries and business leaders who want to patronize Trump's hotel to curry favor with him.

The suit cites a "perception by many of its customers and prospective customers of the hotel ... that it would be to their advantage in their dealings with President Donald J. Trump and other agencies of the United States government if they patronized the hotel."

Pressed at a news conference to provide proof Thursday that the restaurant's business is declining, an attorney said it is "very difficult to put a number on it."

The White House referred a request for comment to The Trump Organization. Alan Garten, a spokesman for the company, called the lawsuit "a wild publicity stunt completely lacking in legal merit."

Previous complaints against Trump and the hotel have focused on the alleged violations of the terms of the lease with the federal government, as well as claims that Trump is violating the foreign emoluments clause of the Constitution by accepting payments from foreign diplomats who stay at the hotel.

But no business competitor had sued Trump while in office until now.

The fact that a restaurant brought this new lawsuit could be significant, as some have questioned whether outside groups have sufficient "standing" -- the legal ability to pursue a case against Trump. In order to bring a lawsuit, courts have said one must show their standing to sue by articulating how you suffered a concrete and particularized injury.

Aside from this new lawsuit, a coalition of ethic watchdogs escalated its concerns on Wednesday, calling on US Attorney Preet Bharara in the Southern District of New York to investigate Trump.

"A failure by your office to investigate these reports and to take appropriate action will leave the nation exposed to foreign governments directly and indirectly providing payments and financial benefits to President Trump when those foreign governments may be seeking to influence executive branch policies and positions," the groups wrote in a letter to Bharara.

Ranking Democrats on two House committees have also asked the inspector general of the General Services Administration to look into situation surrounding the hotel lease.

The Trump Organization leased the property for the hotel from the GSA in 2013, but a clause in the lease states that no "elected official of the government ... shall be admitted to any share or part of this Lease, or to any benefit that may arise therefrom."

Yet the GSA has not declared the Trump Organization in breach of the contract and has consistently declined to comment on the status of any negotiations to resolve the apparent breach since Inauguration Day.

"Because President Trump failed to transfer or eliminate his controlling interest in the property prior to his inauguration, he is now able to negotiate new and favorable financial terms with the administrator he appoints. Left unchecked, this arrangement is fraught with the possibility that President Trump and his children will enrich themselves at taxpayers' expense," the members wrote in a letter on Tuesday.

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