Last month, Donald Trump received some bad news that, naturally, resulted in a Twitter-based tantrum. In a lawsuit filed by Barbara Underwood, the New York attorney general accused the president and all of his adult children of “persistently illegal conduct” related to the Donald J. Trump Foundation. Essentially charging that the charity was used as a personal slush fund, Underwood claimed the Trump Foundation “was little more than a checkbook for payments to not-for-profits from Mr. Trump or the Trump Organization.” The allegations of misappropriation included “extensive support” to the then-candidate’s 2016 campaign, in violation of campaign-finance laws; $5000 being used to advertise Trump Hotels; $10,000 spent on a giant portrait of the president, later found on display at the the sports bar at Trump’s Doral golf resort; and $258,000 that was used to settle lawsuits against Trump and his businesses, including $158,000 paid to a guy who sued the Trump National Golf Club after it failed to pony up a promised $1 million for scoring a hole-in-one at a charity tournament. At the time, Trump claimed that the suit—which seeks to dissolve the foundation, force the president to pay millions in restitution, and temporarily bar him and his three oldest kids from serving in leadership positions at any New York nonprofits—was the work of “sleazy New York Democrats,” angrily insisting, “I won’t settle this case!” And now, a new twist is sure to get him even more riled up.

The New York Times reports that the New York State Department of Taxation and Finance has opened an inquiry into whether or not the Donald J. Trump Foundation violated state tax laws. While officials would not say when their investigation began, or what activities are being looking at, it’s likely that the probe will scrutinize some of the same issues raised in Underwood’s suit. And while Trump has been involved in a whopping 3,500 legal actions (and counting!), this one has the potential to seriously blow up his spot:

A criminal inquiry could reveal additional information beyond the scope of the lawsuit, such as the president’s tax returns. If the investigation found possible criminal activity, it could then refer its findings to a law-enforcement agency, such as the state attorney general’s office or a district attorney. That agency could present the findings to a grand jury, according to the two officials, both senior members of Gov. Andrew M. Cuomo’s office, who spoke on the condition of anonymity to protect an active investigation.

As the Times notes, it’s far too early to say whether the tax department’s findings would ultimately be referred to the attorney general or a district attorney. Plus, when the state attorney general’s office has taken tax-related criminal actions, it’s generally related to things like tax evasion. But the mere fact of the suit cracks the circle of people who have seen Trump’s tax returns—a circle that includes journalist Timothy L. O’Brien and, almost certainly, Robert Mueller—even wider. Given the White House’s steadfast refusal to disclose the information 18 months into Trump’s presidency, that’s sure to irk the not-at-all-compromised commander in chief.