Clarion call vs rallying cry

Solution 1:

While both phrases have the same literal meaning, a request for a group of people to take some action, they have developed different "baggage" that keeps them from being interchangeable. A clarion call can be clearly heard for a long distance and attracts the listener towards it. Think about a siren (in the sense of Ulysses/Homer, not an ambulance), or a sound from a place of worship indicating that it's time to come to services. A rallying cry (cry meaning yell in this context, not weep) reaches a large number of people who are close by and urges them to do something specific, typically to go somewhere else. "Come on! Let's get our pitchforks and get that monster!" These "just a feeling" aspects of distance can also deal with metaphorical distance - a clarion call would be aimed at people who don't agree with a position yet, while a rallying cry gathers those who do agree and motivates them to do something about it.

In your context, not only the word "against" but also the lack of any "hey you, come over here and see this" or "maybe you never thought about this, but you should" connotations make it clear that rallying cry is a better fit. I would generally only use clarion call with to myself.

Solution 2:

The preposition against is rare with both clarion call and rallying cry. I say the problem is with the item writer and not with you.

Solution 3:

I'm going to disagree with the answers posted thus far and say that clarion call is the better choice there. A rallying cry is a short, simple slogan designed to unite people emotionally; to pull two examples from recent U.S. news, "We are the 99%" and "I am Trayvon Martin."

A clarion call, on the other hand, is a clear demand for action of some sort, but it can be short or long and can be presented as more of an argument rather than a slogan. In the context given, the work being referenced is clearly too long to be considered a rallying cry, but apparently presents a case against some particular trend.

Also, as an added context cue, Sound the (x) clearly indicates that "clarion call" is the intended contination; "Sound (a/the) clarion call" gets a significant hit rate on Google Ngrams, while "sound (a/the) rallying cry" gets zero:

Solution 4:

As I understand it, a clarion call is an announcement or warning, with no particular call for action. A clarion itself is a trumpet, used to signal an announcement.

A rallying cry is what it says - a cry, rallying the people for action.

On this basis, as the gap is followed by 'against' I would fill it with 'rallying cry'.