Special counsel Robert Mueller’s ongoing Russia investigation has obtained thousands of emails sent and received by Trump officials during the president’s transition, a move that a lawyer for Trump has decried as illegal, the Associated Press reports. The emails concern 13 top Trump officials, and their correspondence includes national security discussions and chatter about Trump’s possible international goals, according to the report. Mueller’s team reportedly obtained the emails not directly from Trump’s transition team, but from the General Services Administration, a separate federal agency that stored the emails and whose facilities were used by Trump’s transition team. The move has prompted Kory Langhofer, the general counsel for Trump’s transition, to accuse Mueller of using unlawful methods. Langhofer said Saturday that he’s sent a complaint to two congressional committees over the GSA’s “unauthorized” disclosure of materials. His complaints come amid reports of increasing friction between Trump and Mueller’s team, with some lawmakers claiming Trump and his allies are trying to shut down the investigation into whether there was collusion between Russia and Trump’s campaign.