Policymakers should step in to prevent demands on working women dictating how many children they have and when they have them, Constitutional Affairs Minister Harriet Harman is to say.
Ms Harman, who has said she would like to see a female candidate as part of a future leadership team after Mr Blair steps down, is expected to call for "tough action" to give parents stronger rights to choose their hours.
Ms Harman will highlight the dilemmas faced by many working families in society.
These include women feeling they have to have their children later fearing that otherwise they will "lose out" at work; women having fewer children for economic reasons, and women caught between the choice of having as much time as they need to be a responsible parent or achieving the success they could at work."
Speaking at a fringe meeting at the TUC conference in Brighton, Ms Harman is expected to say: "The high cost of childcare and the price that she pays at work if she works fewer hours, mean that many women are stopping at one child when they'd love to have more if they could afford it.
"This is the personal reality behind the "demographic timebomb".
"Public policy should not tell women how many children to have - but it should give them more choice."
Ms Harman will also call for more investment in childcare so that it is not too expensive for families to have more than one child in a nursery.
