U.S. President Donald Trump's pick to serve as commerce secretary, Wilbur Ross, faces tough questions about his possible ties with Russian oligarchs through his position on the board of the Bank of Cyprus.

The Senate is expected to confirm Ross late Monday, and several Democratic senators have raised concerns about the 79-year-old billionaire who specializes in troubled businesses. These questions come at a time when Trump is defending his administration's relations with Moscow, following leaks about repeated contacts between members of his campaign team last year and Russian intelligence officials.

Since 2014, Ross has served as vice chairman of the Board of Directors of the Bank of Cyprus, the largest bank in Cyprus, which was saved from bankruptcy in 2013 by a bailout from the Eurozone countries and the IMF and by forced contributions from most of its savers. This bank also is the second largest shareholder in the Russian conglomerate Lamesa Holding, owned by the Russian oligarch Viktor Vekselberg, whose fortune is valued at more than $12 billion by Forbes.

Ross's predecessor as vice chairman of bank's board is Vladimir Strzhalkovsky, a former KGB agent known to be close to Russian President Vladimir Putin.

"The United States Senate and the American public deserve to know the full extent of your connections with Russia and your knowledge of any ties between the Trump Administration, Trump Campaign, or Trump Organization and the Bank of Cyprus," Democratic Senator Cory Booker said in a letter to Ross.

In mid-February, Booker and five other Democratic senators sent a letter to Ross asking him whether the Bank of Cyprus had lent to Trump's real estate group, the Trump Organization. The officials also called on Ross to reveal whether he had any contact with Russian officials or agents during the presidential campaign.

Billionaire investor Wilbur Ross easily won confirmation as U.S. commerce secretary on Monday, clearing President Donald Trump's top trade official to start work on renegotiating trade relationships with China and Mexico. Ross is set to become an influential voice in Trump's economic team after helping shape the president's opposition to multilateral free trade deals such as the now-scrapped Trans-Pacific Partnership.

Ross, estimated by Forbes to be worth $2.9 billion, built his fortune in the late 1990s and early 2000s by investing in distressed companies in steel, coal, textiles and auto parts, restructuring them and often benefiting from tariff protections put in place by the Commerce Department.