This expression is used when people are strongly encouraged to take action - usually in the context of a conflict situation - to join together in a group to fight off an attack by others, or to promote a cause that seems necessary. (sometimes the expression "call to action" is used - this is similar, but sounds less urgent, less militaristic. It probably originates from times when it was necessary to recruit soldiers to fight against a common enemy (arms in this context = weapons) (the "call" is the appeal to people around: to get their attention). Today it could be used in many contexts, e.g.: "In the face of the incompetence of the government, some opposition politicians have issued a call to arms to prevent the president from being re-elected." This does not imply any violence - it may simply mean encouraging as many people as possible to vote. "With the increasing evidence pointing towards the dangers of climate change, we need a call to arms in order to reverse the present situation." e.g. people in general, or governments, or experts etc. need to get together and act as a group to promote change... "Faced with the imminent extinction of elephants, we need a real call to arms to prevent this outcome." - i.e. a lot of people need to do something to counter the situation.

A call to arms is an appeal to other people to join forces with you against a common cause, or enemy, etc. https://www.merriam-webster.com/dictionary/call%20to%20arms It's a metaphor for calling people to take arms (weapons) and put up a fight against something you disagree with. Note, metaphor. It's not specifically about an actual fight, but often a fight for a cause - petitions, changing the law, etc. In this case, she's asking anyone that agrees to join her in pushing for a change in the pay conditions for women in the film industry. They are putting out a call to arms to people who agree women should be paid the same as men. They want them to join them in their cause.

Thank you all! :)

A call to arms is basically a request for one's allies to come to one's aid in a fight. It's quite formal though. It's often used in a military or historical context, but it can be used in other contexts, such as the two examples that you gave.

Yes it basically mean "a call to protest against something" like you said, more specifically like a call to be prepared for a confrontation. The confrontation can be a protest, or a physical fight. Think of it like this: "a call to arms" literally means a call to ask people to pull out the guns. Which we can understand it as asking people to be prepared for a fight.