I think threatening to quit actually does qualify as extortion according to Wikipedia:
"Extortion, which is not limited to the taking of property, involves the verbal or written instillation of fear that something will happen to the victim if they do not comply with the extortionist's will."
Similarly, threatening to get a divorce, or break up with your SO, if they don't change their behavior, is also extortion under this definition. In fact, any kind of demand for something, or else there will be consequences (such as not buying from that company again, or severing a relationship) can be viewed as extortion it seems.
Hopefully, the actual legal definition is written better than the Wikipedia definition...
"Extortion, which is not limited to the taking of property, involves the verbal or written instillation of fear that something will happen to the victim if they do not comply with the extortionist's will."
Similarly, threatening to get a divorce, or break up with your SO, if they don't change their behavior, is also extortion under this definition. In fact, any kind of demand for something, or else there will be consequences (such as not buying from that company again, or severing a relationship) can be viewed as extortion it seems.
Hopefully, the actual legal definition is written better than the Wikipedia definition...