Speaking via an online link to the House, Labour MP for south London's Lewisham and Deptford boroughs and Shadow Minister for Disabled People Vicky Foxcroft began by signing first, before questioning the lack of interpretation available at the new £2.6 million briefing room.
"And if the Prime Minister doesn't understand, imagine how those who rely on British sign language feel at his press briefings," said Foxcroft.
"£2.6 million spent on the new press room, yet still no interpreter," she added. "What message does he think this sends to disabled people?"
Johnson thanked the MP for her question and promised to "revert" to her as soon as possible.
From end of March the British government has hosted White House-style televised briefings for journalists in the specially refurbished studio space.
Due to open in autumn last year, the cost of the new press room has attracted criticism, including from Labour shadow minister Rachel Reeves who described it as "a vanity project", according to the BBC.