Homeland Security Secretary Alejandro Mayorkas will face Congress on Tuesday with a host of pressing questions about terrorism and border security — but one senator also plans to challenge him on his use of a private email to conduct government business.

Sen. Roger Marshall, Kansas Republican, has been pressing Mr. Mayorkas about his email practices for months and has grown frustrated with the lack of responses. With the secretary appearing in person, Mr. Marshall is determined to get answers, according to his planned questions, shared exclusively with The Washington Times.

“The sheer volume of communications on your private email and cell phone raises serious concerns about whether all official messages sent to or from these devices were properly forwarded back to your official DHS accounts. The volume of messages also calls into question your insistence that anything you have ever received in your personal email address was sent ‘errantly,’” Mr. Marshall will say.

Homeland Security, in a statement to The Times, said Mr. Mayorkas is following the rules and does his official business on his official account.