be up in arms
to be very angry and ready to argue or fight

[TahlilGaran] Dictionary of Contemporary English ▲

up in arms
very angry.
Local businessmen are up in arms over the new parking regulations which will make shopping very inconvenient for customers.

Usage notes: often followed by a phrase beginning with over, as in the example, or about:
Why aren't we up in arms about children who are not being educated?

[TahlilGaran] English Idioms Dictionary ▲

up in arms
equipped with guns or weapons and ready to fight, very angry; to be very angry and wanting to fight
The villagers were up in arms over the proposal to take some of their land away from them.

The students were up in arms over the school's plan to make them wear uniforms.

[TahlilGaran] English Idioms Dictionary ▲

up in arms
adj. phr.
1. Equipped with guns or weapons and ready to fight.
All of the colonies were up in arms against the Redcoats.
Synonym: IN ARMS.
2. Very angry and wanting to fight.
Robert is up in arms because John said he was stupid.
The students were up in arms over the new rule against food in the dormitory.

[TahlilGaran] English Idioms Dictionary ▲