Exodus 1:9-11

9 And he said unto his people, Behold, the people of the sons of Israel [are] more and mightier than we.

10 Now, therefore, let us be wise concerning him, that he not multiply and it come to pass that when war comes, he shall also join with our enemies and fight against us and [so] leave the land.

11 Therefore they set taskmasters over them to afflict them with their burdens. And they built the supply cities for Pharaoh: Pithom and Raamses.