Federal lawmakers concerned about gambling addiction are starting to scrutinize online betting companies’ targeting of big spenders and VIPs.

Sen. Richard Blumenthal (D., Conn.) sent letters last week to eight online gambling companies, including FanDuel and DraftKings, urging them to stop using player data and other marketing tactics to target customers with gambling problems.

He noted The Wall Street Journal’s report last month profiling a psychiatrist who tried to quit online gambling but lost more than $400,000 in less than a year, egged on by perks and thousands of dollars in betting credits doled out by VIP hosts.

“Gambling addiction is so pernicious because it is so prevalent and so rampantly denied as a problem,” Blumenthal said in an interview.