> ... population has grown... ... number of people immigrating depends primarily on the labour market. When the economy is strong, companies... often recruit the ... workers they need from the EU.

> ...

> The... sustainability initiative...[:] If the permanent resident population exceeds 9.5 million ... the Federal Council and Parliament will need to take measures, particularly in the areas of asylum and family reunification.

So, this measure says that if companies need more workers, Switzerland will refuse to grant asylum, and will prevent Swiss residents from having their spouse, child or parent come live with them.

Regardless of whether population capping is legitimate or not, that sounds quite nasty. If the measure had said "in case of population growing, there will be a moratorium on recruiting employees from abroad", then you would have a discussion.