Almost 200 Democratic lawmakers are suing President Donald Trump over foreign money flowing into his global business empire.

A total of 196 senators and representatives are plaintiffs in a lawsuit alleging Trump is violating the so-called emoluments clause of the Constitution.

It is to be filed early on Wednesday in US District Court for the District of Columbia, the lawmakers said.

The plaintiffs argue they have standing to sue because the clause says only Congress may approve foreign gifts and payments.

Almost 200 Democratic lawmakers are suing President Donald Trump over foreign money flowing into his global business empire. Trump is pictured on Tuesday in Wisconsin

'The framers gave Congress a unique role, a unique right and responsibility,' Connecticut Senator Richard Blumenthal said.

Although Trump turned over control of his real estate development, management and marketing company to his adult sons and a senior executive, he did not divest from it.

That means he stands to benefit financially from the Trump Organization's profits, including from foreign governments.

Since he has become president, the Trump Organization has secured dozens of potentially valuable patents, including in China, and collected fees from lobbyists working for Saudi Arabia and other countries using his properties.

The new suit - the third of its kind - said the full scope of foreign payments to the Trump Organization cannot be known because the president has not made public his tax returns.

Earlier this week, two Democratic attorneys general filed a similar claim. Days after Trump's inauguration in January, a liberal-funded government watchdog filed an emoluments lawsuit.

'The framers gave Congress a unique role, a unique right and responsibility,' Connecticut Senator Richard Blumenthal said

John Conyers, a Michigan Democrat, said he and Blumenthal have amassed the 'greatest number of congressional plaintiffs on any lawsuit against a president' - adding Trump 'left them with no other option'

A restaurant group and two individuals in the hotel industry later joined as co-plaintiffs.

Trump and the Justice Department have called these lawsuits baseless.

They argue the clause is not intended to prevent normal business such as hotel payments and real estate transactions.

John Conyers, a Michigan Democrat, said he and Blumenthal have amassed the 'greatest number of congressional plaintiffs on any lawsuit against a president.'

He said they're taking the action 'not out of any sense of pleasure or partisanship but because President Trump has left us with no other option.'

Ahead of the filing, only Democrats were asked to sign on, but Blumenthal and Conyers plan to send letters to their Republican colleagues Wednesday asking them to join the effort.

Donald Trump waves as he makes his way to board Air Force One before departing from Newark Liberty Airport in Newark, New Jersey on June 11

In a motion to dismiss one of the similar lawsuits last Friday, the Justice Department argued plaintiffs had not shown any specific harm to their businesses, while claiming Trump was only banned from receiving foreign government gifts if they arose from his service as president.

On Monday, White House press secretary Sean Spicer said 'partisan politics' was behind the lawsuit by the Maryland and District of Columbia officials.

Lawmakers rarely sue the president, so there are few federal court decisions the legislators can cite to prove their legal standing to bring Wednesday's case, said Leah Litman, an assistant professor specializing in constitutional law at the University of California, Irvine.

'But the constitutional provision they're suing to enforce gives them a role in how it's carried out, and that gives them a powerful standing argument,' Litman said.

The lawmakers in Wednesday's lawsuit will be represented in court by the Constitutional Accountability Center, a public interest law firm in Washington. Each lawmaker is paying a share of the legal fees from personal or campaign accounts.