http://idioms.thefreedictionary.com/force+hand

We didn't know what she was doing until Tom forced her hand. We changed our game plan after we forced the other
I'm sure they don't want to reduce the price but if you threaten to pull out of the sale that might force their hand.
Information dug up in the investigation forced the president's hand, and he resigned much sooner than anyone expected.

If you force someone's hand, you make them do something unwillingly or sooner than planned.

you leave me no choice

You brought me before finished spell

You leave me no choice.