According to The New York Times, the Justice Department has issued a subpoena to former senior White House advisor Stephen Miller.
More than a dozen people with ties to Trump, including Miller and the former White House political director Brian Jack.
The Times reported earlier this week that subpoenas were issued to several "junior and mid-level" advisers who worked for Trump in the White House and for his presidential campaign.
A person familiar with the subpoenas told CNN that they stem from a federal grand jury investigation into whether or whether Trump's Save America PAC.
OpenSecrets.org, an organisation that keeps tabs on political contributions and spending, claims that the Save America PAC has raised nearly $103 million.
According to the Times, the subpoenas seek evidence related to an alleged plot to send electors to battleground states in an effort to alter the results of the election.