Exodus 5:1-7:6
It's tempting, in our contemporary mindset, to view Pharaoh as an atheist mocking the idea of a 'god,' but this was surely not the case. Pharaoh and the Egyptians believed in many gods. His response "Who is the Lord" is a question of whether Lords existed, but which specific Lord was being spoken of. Why should Pharaoh respond to a god whom he had never heard about?
It's curious as to why Moses doesn't, at this point, use the 'tricks up his sleeve' (so to speak). Perhaps God didn't want him to display His power yet. In any case, in the absence of a more convincing argument, Pharaoh increases the workload of the Israelite slaves. These slaves had been building, but the straw to make the bricks had been provided for them by the Egyptian government. From this point on, they would have to gather their own straw while maintaining their brick making quota. Archaeological digs (Naville) confirm that the city of Pithom (Exodus 1:11) does indeed contain buildings with strong brick/straw bases. But the higher up on the buildings you examine, the quality decreases, lending evidence to the historicity of this account.
The Hebrew foremen must have figured Pharaoh was unaware of these impossible demands because they decided to appeal to Pharaoh for help. They realized, however, that Pharaoh himself was behind the increase. At this point they knew they were in real trouble. They couldn't work the workers any harder. They couldn't get help from Pharaoh. No one was left to blame except Moses (5:21).
Moses must have felt like God had tricked him (5:23). Moses had rallied the Israelite community and made a bold request of Pharaoh, but to no avail. Pharaoh said no. The Israelites were now against Moses again? Why had God allowed this? A vital lesson is learned here: Obedience to God doesn't mean life will get easier. On the contrary! It may mean life will get harder.
God reassured Moses that His plan was still in process, but Moses has no confidence because he sees no results (6:12). After being given a genealogy (for historical purposes), we are given some insight into why God is allowing the events to proceed in the manner in which they were. Out of these troubles 2 things would happen: 1) The Israelites would come to a greater understanding that God is God (6:7) and 2) The Egyptians will come to an initial understanding that God is God (7:5). This was a hard process for Aaron and Moses who were 83 and 80 respectively.