Yes, sorry I was still editing that. This is obviously the NGO's point of view which is different from the miners point of view.

Passing a law like this is no small feat; it probably had lots of support from the population countering all the corporate pressure against it.

Upon some research, seems like even the catholic church was in favour [1], which is what gave it the final push. I doubt this will cause problems to the level of starting riots; rioting against the government is one thing, but having your church and larger community against your cause definitely makes it lose momentum.

[1] http://www.bbc.com/mundo/noticias-america-latina-39451498

Though El Salvador is no stranger to having popular governments overthrown by corporate interests.

Sure, the miners are going to be unhappy. But "massive" is not a subjective judgment; I trust the NGOs on the numbers, and if so the miners are not a large enough population that their firing is a threat to social order.