in league (with someone)

In close, often secretive or conspiratorial cooperation with someone. It turned out that the business tycoon was in league with local law enforcement to have the investigation dropped. We've been in league with a company overseas who can produce the product for half the price.

Fig. [of people] secretly cooperating, often to do something bad or illegal. The county sheriff is in league with criminals. The car thieves and some crooked police are in league to make money from stolen cars.

Also, in cahoots with. In close cooperation or in partnership with, often secretly or in a conspiracy. For example, "For anybody on the road might be a robber, or in league with robbers" (Charles Dickens, A Tale of Two Cities, 1859), or We suspect that the mayor is in cahoots with the construction industry. The first term dates from the mid-1500s. The variant, a colloquialism dating from the early 1800s, may come from the French cahute, "a small hut or cabin," and may allude to the close quarters in such a dwelling.