Many companies use discounting as a way to boost sales, admittedly Oil co.s don't really need to do this because of the demand for their product.
But if they wished to do so as a marketing strategy, then no police force on the planet would arrest them. Shareholders will only care if the profits fall, or the company loses money. Very rarely do shareholders have a say in the day to day running of a business.
If the discounting strategy was a failure and a company lost money, then the shareholders may kick up a stink, but you don't call an EGM everytime you want to make a decision in business.