If it's illegal you're in a situation where the landlord likes money and the tenants like not being homeless. In a house where 4th amendment rights are strongest.

In practice I think it's about impossible to enforce. Code enforcement or police would need a warrant to enter, and in most jurisdictions the complaints are public record far enough ahead of time anyone with the slightest bit of foresight would get ahead of it.

In my county sometimes I monitor the local complaints, mostly initially when I was looking at properties because I did not want to live next to a neighbor who likes to be a busybody to the code enforcement. There are a number of properties that just lock their gates whenever a code complaints happen or tell code inspection to kick rocks, by the time they come back with a warrant the situation is faked well enough they can't do anything.

>In practice I think it's about impossible to enforce. Code enforcement or police would need a warrant to enter

If they have a suspicion and they feel inclined to go after you they'll just go hard enforcing all manner of other shit they don't need to go inside to enforce agains the landlord. It doesn't matter that the things they're trying to enforce may very well be bullshit that couldn't stand in court if challenged, it's cheaper to comply than to fight it.

Code enforcement and other civil and administrative areas of law where the .gov can issue fines on the same order or larger than many criminal penalties while giving the accused none of the rights of criminal trial are a massive, massive, massive, I can't say it enough, massive, end run around constitutional rights.