Revolutionary Front

Revolutionary Front is a splinter group of the Imperial Magic Guild that split off about two hundred years ago, although it has ideological roots dating back to the Second Era. The creators of the Revolutionary Front were inspired by numerous writers describing a world of an actual equality. Not only political one (which means both no slavery and no nobility), but also one where access to magic will be unrestricted, and all citizens will be mages, if only of the first Circle.
What was reasonably achievable during the Second Era (and not achieved only due to the general population having a rather apathetic approach to learning what was perceived as combat skills in an era of peace, as the Ascendant Conclave hoarded the more industrial uses of magic), is an absolute utopia during the times of the Third Era. The Grand Empire simply cannot hope to achieve any reasonable degree of equality in a situation where the Shattering has limited certain resources and certain production facilities only to certain provinces (and leading to the resulting goods becoming luxury ones by default in other provinces, since sending them there requires a trip through almost literal hell). And that's without mentioning its administrative capabilities (which are strained almost to the breaking point) and the constant warfare.
This doesn't the Revolutionary Front from trying. Of course, not all of its demands are completely baseless and insane - for example the forbidding of slavery is something that would get a lot of support, and not only from the slaves themselves. The real problem is that the Front is, well, revolutionary - it is trying to achieve said goals through inciting popular rebellions or riots, and is creating new mages (and sorcerers) en masse. Which is a problem since without strict oversight during their training and some proper moral guidance, they tend to fall surprisingly quickly and end up flooding nearby forces of the Fallen en masse. Boosting them greatly.
In the end, the Front is mostly a nuisance. One that caused hundreds of thousands of casualties throughout the ages, but rarely amasses sufficient firepower to be able to become a more existential problem to even a small region of the Grand Empire. This doesn't stop the Grand Empire from considering the Front to be a terrorist organization and do its utmost (with the Imperial Magic Guild being especially zealous on that field) to eradicate it. However, it persists.

Structure

Like other splinter factors of the Imperial Magic Guild, the Revolutionary Front maintains a relatively similar internal organization. There are always its headquarters, hidden somewhere in the Lost Lands near a province, from which local cells (responsible for recruitment, incitment of the masses and gathering of resources) are controlled, with the messenger between them often being adventurers. All of that is a singular, self-governed suborganization, that responds to a mysterious headquarters of the Front as a whole.
Only the heads of such regional suborganizations are allowed access to said headquarters, and even they do not know where it is (they are kept unconscious for the duration of the travel), with the messages to and back from it transferred with magical means. It is said to be an ideal city (from the point of view of the Front's ideas) located somewhere deep in the Lost Lands, were all are equal and all are mages. However, many suspect this city to be a fabrication, and the 'unconscious' state of the leaders meaning that whoever's truly leading the Front has time to brainwash them with fake memories. If it's true, then whoever's responsible for the whole thing has did a great job hiding all evidence.

Military

From the military point of view, the Revolutionary Front has little to show. They can often incite large crowds of rioters, including some that has earlier received a low-level training in martial arts or magic. These 'crowds' are sometimes numerous enough to overwhelm the law enforcement, adventurers and other armed forces of some towns and cities sometimes in a majority of a province if situation there is bad enough. However, this is rarely enough to maintain the control over the region for long.
Unless an entire province (typically praesidial) is overwhelmed, which is when it changes into a way more long-term holding of the Revolutionary Front. There are a handful of those existing, with the wide-scale appearance of mages (many of whose are falling) typically meaning that retaking such a province is considered not worth the effort (although the Empire will typically launch some raids to recover technological relics and other somewhat important things left in the province). Of course, the numerous armies of the Fallen might think otherwise, which tends to be the end of such provinces.