Throw down the gauntlet
Definition 1 of 1
Pro Tip 1/3Historic Origin
The phrase originates from medieval times when knights would throw down their gauntlet glove as a challenge. 
At the renaissance fair, the actor would dramatically throw down the gauntlet, inviting visitors to a mock duel.
Pro Tip 2/3Figurative Use
Today, the phrase is used figuratively and does not involve an actual glove or physical challenge. 
The CEO threw down the gauntlet to her competitors with her bold new business strategy.
Pro Tip 3/3Conflict Implication
Using the phrase suggests a readiness for some form of contest or confrontation. 
By rejecting the terms, they effectively threw down the gauntlet to the negotiation team.