Members of the Upper Chamber are expected to table the motion as early as today with a debate and vote planned for next Tuesday.
The move will come as an embarrassment to the Prime Minister, who in reshuffling could only make room for Baroness Stowell, the Lords leader, around the Cabinet table on a part-time basis.
Also, she faced a cut in pay compared to her male predecessor. But the Tory Party has offered to make up the difference. Mr Cameron faced difficulties because there is a cap on the number of full-time members of the Cabinet and a ceiling on the total pay.
The Upper Chamber heard how his decision was a "constitutional outrage". Lord Forsyth, the former Conservative Scottish Secretary, insisted it was "vital" for the Leader of the Lords to be in the Cabinet full-time.
Last night, Baroness Royall, the Shadow Leader, said: "He reshuffled his Cabinet to raise the profile of women, which is good, and then offered a top post to a woman but demeaned her by not giving her the same status as the two men he appointed previously."