India is preparing for a once-in-a-generation redraw of its political map, driven by what the government says is a push to reserve one-third of seats for women in parliament and state assemblies.

To do that, the government will unveil a constitutional amendment - requiring a two-thirds majority - backed by a three-day special session from Thursday.

Women make up only about 14% of India's 543 lower house MPs. The reform would raise that to roughly a third, closer to global norms.

Its rollout is now tied to a population-based redraw of constituencies based on the 2011 census - likely expanding the lower house from 543 to about 850 seats.

But this has fuelled controversy, with opposition parties accusing the government of rushing changes during an election season.

India already reserves 33% seats for women in village councils and municipal corporations in urban areas.

Prime Minister Narendra Modi has cast the Nari Shakti Vandan Adhiniyam (which loosely translates from Hindi to Saluting Women Power Act) as a historic leap - among the most significant decisions of our times - arguing it honours women's empowerment.

Opposition parties say a simple women's quota is being tied to a controversial redraw of constituencies, turning a gender reform into a wider political overhaul.

The Modi-led Bharatiya Janata Party (BJP) government has signalled a break from past caution, proposing a fresh delimitation based on the 2011 census, which has alarmed opposition leaders who fear it could cost them seats and influence, especially in the more prosperous southern states of India.

Critics also question why the exercise is based on 2011 data amid calls for a new census, with the government countering that delays could push women's reservations beyond 2029.

Amid these challenges, the ultimate effectiveness and fairness of the proposed reforms remain a contentious topic among stakeholders.