Ask HN: What methods of information gathering are legal under congressional law?

Outside of the conversation of our shared popular desire for everyone to not know our every action.

The forth amendment only applies to criminal law, covertly gathered information can't be used in criminal proceeding. My question -> What does the actual congressional law say in regards to the power of governmental supervision in civil matters? This has business implications not just regarding government contracts to purchase information but also to the tracking hooks that web companies use to power preference engines.

We can have another feed asking the question of who is best at playing the good shepherd with our personal information? public or private sector? Or to suppose the preferences of congressional members desire to be NSA briefed on the opinions of their constituents.