unions

Unless you control supply, then you can create artificial scarcity.

There's also the common way where large corporations kill smaller companies or local businesses by predatory pricing techniques, then when those are under, they absorb the business and hike prices.

As manual labour goes, if your market is controlled by a single entity, then even if there's large demand for you, you won't have a chance in getting good conditions.

The same goes if you're a contractor or a small company where your client controls the market.