Special counsel Robert Mueller’s investigation may be homing in on Donald Trump’s business dealings. The New York Times’s Michael Schmidt and Maggie Haberman report that Mueller has subpoenaed documents from the Trump Organization, including some related to Russia.

Recent reports have suggested that Mueller has turned his attention to some of Trump’s business activities, including his past attempts to build a Trump Tower in Moscow. But this is the first time the special counsel has gone after documents from the Trump Organization, which might be a sign that he’s delving deeper into this line of investigation. It’s also an indicator, as the Times notes, that the special counsel probe is far from complete.

It’s not clear exactly what’s covered by the subpoena, Schmidt and Haberman write, or why Mueller issued a subpoena rather than requesting the documents. CNN reported in February that Mueller was questioning witnesses about Trump’s 2013 trip to Moscow and asking about when he decided to run for president. The probe has also broadened to include foreign business dealings from people in Trump’s orbit, particularly son-in-law Jared Kushner.

Either way, this once again sets up a possible showdown between Trump and Mueller. Trump has previously said that his finances are outside the mandate of the special counsel, and his ire toward the Russia investigation is no secret.

Trump has attempted to fire Mueller before; if he perceives Mueller as poking around in an area that he considers off limits, it might put the special counsel in jeopardy once again.