If you want the neoclassical version:

What happens when there is an oligopoly in the supply of labor?

Same answer. Nothing good for the consumers of labor.

(See Medicine)

Technological improvements shift supply curves right which is good for consumers.

In a market with perfect competition, which I specifically ruled out by stating that the suppliers of labor from an oligopoly.

Why would you expect technological improvements to only shift supply curves right under perfect competition? I'd also expect it under oligopoly or even monopoly. You also might think there'd be more tech improvement under oligopoly, on Schumpeterian grounds that oligopolists can internalize the benefits of tech research.

A monopolist has no reason to decrease price because there is no competition. As we saw with Bell Labas in the US it is entirely possible for a monopoly to both have world class research and burry it for decades, viz. magnetic storage https://gizmodo.com/how-ma-bell-shelved-the-future-for-60-ye...

Oligopolists are in the same boat. But there needs to be a conspiracy to retard innovation. Something tech companies are only too happy to do: https://journals.law.unc.edu/ncjolt/blogs/wage-fixing-scheme...

Technological improvements don't reduce prices as much in a monopoly, but they still do reduce prices to increase profits. Profit is always maximized at MR=MC, in perfect competition, oligopoly, or monopoly.