I mean landlords would do that.

Here in Sweden we have a pretty democratic system set up. There's a nationwide tenants union that negotiates rents with the landlord union, and there's a third "arbiting" party that also deals with disputes between the two. Landlords are free to set more or less whatever rent they wish, but a tenant can claim that the rent is too high, and if it's found to be true the landlord can be made to pay their tenants back.

The rent negotiations happen once a year, and stretches over the course of several months. Generally they start towards the end of the year, and sometimes they drag on. My previous landlord didn't finish negotiating until June or July I believe - and they require the rent retroactively too. Fuckers.

Anyway, this year the economy's been quite bad. The landlords screamed that they need a much higher increase than usual, to keep their head above inflation. Mind you, past few decades they've always had rent increases above inflation, but now they were asking for a ridiculous number, like 10-15% increase. The tenants union managed to negotiate this down, we still saw record high increases but more along the line of 5-8% or so.

Then some greedy bastards decided, let's just raise the rent a second time this year. There'd been a poll, and tenants had basically responded "yes, we're expecting large rent increases next year too", which the landlords used to motivate the second increase saying "well they expect a large increase so they're ready and willing to pay for it." As though expecting an asshole to be an asshole somehow means you're OK with them being an asshole.

I believe they were forced to repay the tenants the additional rent they'd tacked on, but the "final battle" about it hasn't been had yet.

Basically, landlords are scum even in a system that actually gives tenants rights. Landlords shouldn't exist.