Union Government
Upon the completion of each census, the allocation of seats in the House of the People to the States and the division of each State into territorial constituencies shall be readjusted by such authority and in such manner as Parliament may by law determine, subject to provisos protecting the sitting House until dissolution and freezing readjustment until specified future census figures are published.
After every census, Parliament seats are supposed to be redistributed among states to reflect population changes - but a series of constitutional amendments have frozen this readjustment for decades (originally tied to the 1971 census figures) specifically so that states successful at population control aren't penalised with fewer seats relative to states with less controlled population growth.
This freeze is why Lok Sabha seat numbers have remained largely based on 1971 population data for decades even as India's population and its distribution across states has changed dramatically since then - a long-running, politically sensitive issue often called the "delimitation" debate.