Swiss pharmaceutical behemoth Novartis said it made monthly payments to Cohen's company, Essential Consultants, totaling $1.2 million for guidance "as to how the Trump administration might approach certain US healthcare policy matters." Novartis said it determined Cohen was "unable" to provide the desired services after a meeting in March 2017.

Telecommunications giant AT&T said in a statement last week that it paid Trump's attorney, Michael Cohen , $50,000 a month under a one-year contract brokered shortly after the 2016 election to gain insights into the new president and his administration – including on regulatory issues and the company's deal to merge with Time Warner .

Senate Democrats sent dozens of questions to AT&T and Novartis on Monday, saying the multinational companies' recently revealed payments to the company of President Donald Trump 's lawyer "raise obvious questions about corruption."

The letters sent to the two corporations were led by Sen. Elizabeth Warren, D-Mass., and signed by Sen. Richard Blumenthal, D-Conn.

Sen. Ron Wyden, D-Ore., sent his own questions to Novartis' CEO on May 11, and signed Warren and Blumenthal's letter to AT&T.

Both letters say that the "unusual" series of payments to Cohen's company raise questions about a potential "pay-for-play operation" involving the companies and the Trump administration.

AT&T and Novartis did not immediately respond to CNBC's requests for comment on the Democrats' letters.

Payments from multiple companies to Essential Consultants were first publicly alleged in an explosive report from lawyer Michael Avenatti, whose client, porn star Stormy Daniels, is suing Trump and Cohen to void a nondisclosure deal that bars her from discussing an alleged sexual encounter.

Cohen created Essential Consultants in October 2016, shortly before he paid Daniels $130,000 as part of the agreement.

Lawyers for Cohen said in a later court filing that Avenatti's report contained "numerous inaccurate statements," including attributing payments to Trump's lawyer that were actually sent to different people also named Michael Cohen. Avenatti pushed back on Twitter, saying Cohen's lawyers failed to address "99% of the statements in what we released."

Avenatti tweet

Cohen was also hired by investment management company Columbus Nova "as a business consultant regarding potential sources of capital and potential investments in real estate and other ventures," according a statement from the company. The company is linked to Viktor Vekselberg, a Russian oligarch has been sanctioned by the U.S.

"The claim that Viktor Vekselberg was involved in or provided any funding for Columbus Nova's engagement of Michael Cohen is patently untrue," Columbus Nova said.