Subsidies are irrelevant to price supports, and unionization helps negotiate the price support levels but even ununionized farmers benefit from price supports. The government does a whole lot of things to keep farmers alive because the food they farm is worth nothing. They force them to sell it at a higher value than the equilibrium price would be, this is called a price floor or price support. They give the farmers free money for farming, this is called a subsidy. They also take a huge chunk of crops out of the market. They used to just burn it, but people got up in arms about that because there were starving people in the world and they were just wasting food. Now they package that food as what's called commodity food and give it to places like schools and shelters where it can be used to benefit people yet not affect the market. They also legislate the amount of food that farmers are allowed to grow and how often farmers must leave fields to lay fallow before they can use it for growing food again.
The issue is, food is worth way less than we pay for it. If the government stopped doing all these things to increase the price of food, we'd be paying pennies for fruit instead of quarters. The income of farmers would drop extremely drastically, so much so that they wouldn't be able to support themselves. They'd default on the loans they took out to start farming that year (which nearly every farmer does) which would shake the economy. They'd have to sell their farms and their houses to try to move somewhere they can get a job doing something else. As all the farms started to shut down, the food supply would hit a critical low and there wouldn't be enough food to go around and people would start starving. The price would start to rise because of the lack of supply, but it'd take a serious amount of time until people started farming again after they just gave up their farms. During that time, most people wouldn't be able to afford food.
TL;DR: gov keeps people from starving by overpaying farmers.
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