Construction company raise price after contract?

[Nikki Bai]

Hi Investors,

I signed my first investment property contract back in March this year. While today, the construction company told me to either accept a $42000 increase on top of the contract price, or get off. I understand now it's a seller's market and the cost is rising, but still, is this a common practice? 

If it is, what can I do in future to protect myself from this?

Happy investment!

Nikki