If you are using a normal Sol System start, it can be prudent to set Earth (your primary source of colonists) as a Destination, not merely Stable. The Stable setting still allows for the transfer of colonists, but at what is supposed to be a much lower rate, and it does NOT stop Luxury Liners from pulling colonists.
So long as every sizable source of colonists is set as a Destination, no colony ships will be able to pull people from anywhere at all.
One way to take advantage of this is to have multiple colonies of more than 25 million people. Simply alternate which colony is a Destination and which one is a Source. Civilian shipping will then generate tax revenue for you by moving lots of people from one to the other. Once the current Source drops below 25 million people, it defaults to a Destination, meaning that no colonists will be moved from it. When you notice this, and want to give the shipping lines something to do, you reverse the settings.