In the world of payments, casinos are highly-complex players, with an unusually high mix of cash and cross-border transactions. That’s one of the reasons federal investigators are probing Wynn Resorts for various money-laundering issues, according to a report in The Wall Street Journal.

The story said that a letter sent to Donald Campbell, Wynn’s outside lawyer, by the IRS criminal investigation division in August requested information on Wynn’s U.S. and foreign clients, its domestic and overseas marketing offices, and its internal controls.

“The letter, which was reviewed by The Wall Street Journal, asked the casino for a list of its biggest customers from 2011 through 2013, along with their dates of birth, Social Security numbers and details from their identification documents. The IRS specified it wants information about the company’s safeguards against money laundering and requested a list of Wynn’s top 100 patrons from North America as well as its top 50 in each of three other regions: Asia, Europe and Latin America, according to the letter. In the letter, the government also asked for an organizational chart of Wynn senior management and staff working in casino and credit operations. The IRS asked for details of branch offices in the U.S. and abroad that enroll customers into credit programs.”

Since the mid-1980s, casinos have had the same obligations as banks to report large cash transactions. “Casinos ‘must continue their progress in thinking more like other financial institutions’ to identify money-laundering risks, said Jennifer Shasky Calvery, the director of the Treasury Department’s Financial Crimes Enforcement Network, or Fincen, at a conference in June,” the story noted.