Special counsel Jack Smith, who is investigating former President Donald Trump’s handling of classified documents, is leaning up pressure on one of Trump’s lawyers to testify before a grand jury, a person familiar with the matter told CBS News Thursday.

Prosecutors argue that they need to learn more about an alleged June 24, 2022, call between Trump and his lawyer, Evan Corcoran. At the time, investigators were seeking to secure documents at Trump’s home and video surveillance tapes of Mar-a-Lago.

ABC News first reported that investigators were seeking to question Corcoran.

The person familiar with the investigation told CBS News that prosecutors wanted to know what Trump might have said during the alleged conversation, and whether he gave Corcoran any orders about how to handle subpoenas.

The chief judge overseeing the case is expected to make a decision on whether Corcoran will be compelled to testify about the call in the coming days.

Corcoran has appeared before a grand jury, but has so far refused to answer questions on his communications with Trump, claiming attorney-client privilege.

Prosecutors are now seeking to use the “crime-fraud exception” to compel Corcoran to testify about his client, Trump, and the former president’s conduct around the time Mar-a-Lago surveillance footage was ordered to be submitted to investigators through a subpoena.

Under the “crime-fraud exception,” attorney-client privilege would not apply if the discussions were in furtherance of illegal activity.

Key questions remain about how Trump responded to federal document requests and what he said to his attorneys before and after the FBI first searched Mar-a-Lago in August, according to a second person close to the investigation.

Smith was appointed special counsel in November to oversee the Justice Department’s criminal investigation into Trump, which includes his handling of sensitive government documents and the possible obstruction of efforts to retrieve them, as well as efforts to interfere in the 2020 election.

Trump, who denies wrongdoing, has not been charged.

Corcoran was unavailable for comment when reached by CBS News.