Exodus 1:12 (KJV)

Come on, let us deal wisely with them; lest they multiply, and it come to pass, that, when there falleth out any war, they join also unto our enemies, and fight against us, and so get them up out of the land.

Therefore they did set over them taskmasters to afflict them with their burdens. And they built for Pharaoh treasure cities, Pithom and Raamses.

But the more they afflicted them, the more they multiplied and grew. And they were grieved because of the children of Israel.

And the Egyptians made the children of Israel to serve with rigour:

And they made their lives bitter with hard bondage, in morter, and in brick, and in all manner of service in the field: all their service, wherein they made them serve, was with rigour.