The government proposes to reduce the number of MPs from 650 to 600, in the process making the number of voters in each constituency vary much less than it does now.
This has proven to be one of the most divisive parts of the coalition's constitutional reform programme, with ministers facing accusations of gerrymandering.
Why equalise constituency sizes?
In 2010, the number of voters in some constituencies diverged by over 30% from the average. Some votes are therefore worth less than others, the government argues, and the move will make general elections fairer.
But Labour says the change is motivated by party political advantage, since Labour MPs tend to represent constituencies with fewer voters and therefore will lose out most from the changes. The SNP and Plaid Cymru have complained that Scotland and Wales face the highest proportional decrease in MPs, with Scotland losing seven out of a current total of 52 seats and Wales losing 10 out of 30.
The government maintains that these arguments represent a ruse to maintain a current unfair electoral advantages.
How many MPs should there be?
The government believes that cutting the number of MPs by 50 is manageable and will produce considerable savings. But some MPs wonder whether their constituents will be adequately served by MPs with increased constituency workloads.
Before the general election, both the Lib Dems and the Conservatives proposed cutting the number of MPs - to 500 and 585 respectively. So why, Labour asks, did they then decide on 600? Shadow minister for political and constitutional reform Chris Bryant says the figure seems to have been "plucked out of the air".
Why the hurry?
Labour has also criticised the coalition for scrapping public inquiries into boundary changes and pushing ahead with the boundary review while millions of eligible voters remain unregistered on the electoral roll. The party also notes that unregistered voters tend to be younger and from ethnic minority backgrounds, prompting accusations of gerrymandering.
The government counters that Labour failed to make enough progress on boosting voter registration when it was in power. The boundary review must be completed rapidly, it says, so that the principle of fairer votes will apply at the next general election, planned for 2015.
Shouldn't there be fewer ministers too?
The government has also provoked the ire of some Conservative backbenchers by failing to reduce the number of ministers in Parliament in line with the reduction in MPs. The executive's influence over the legislature will increase, they argue.
As MPs debated the legislation, deputy Commons leader David Heath recognised that the matter "deserved consideration" and pledged to bring forward plans to address it in due course.
What about historic, geographic or cultural barriers to constituency equalisation?
Ministers have conceded that there is a case to exempt four constituencies from the equalisation process: Na h-Eileanan an Iar (the Western Isles), Orkney and Shetland, and two Isle of Wight constituencies - for geographical reasons.
However, historic and cultural considerations, such as the border between Devon and Cornwall, will not be allowed to over-ride the Electoral Commission's efforts to bring the number of constituents to within 5% of the average.
Critics worry that MPs may struggle to represent constituents on both sides of cultural divides in future, and may face longer journey times around larger constituencies.