Federal Regulations

Affordable Care Act
Americans with Disabilities Act
Clinical Laboratory Improvement Amendments (CLIA) 
False Claims Act (Auditors: MACs, RACs, ZPICs) & Stark Laws
Health Insurance Portability and Accountability Act (HIPAA)
Health Information Technology for Economic and Clinical Health (HITECH) Act
Health Maintenance Organization Act of 1973 (Lots of state specific variation)
Laboratory Client Billing Restrictions (typically state law based)
Medicaid: A Full Analysis
Medicare Opt Out Regulations
National Practitioner Data Bank
Occupational Safety & Health Administration (OSHA)
Patient Brokering (Fee Splitting & Corporate Practice of Medicine)
Pathology Services Restrictions (actually state law based)
Sunshine Act
Tax Treatment of DPC

Federal Legislative Efforts

See the Direct Primary Care Coalition website - federal policy efforts include: 
Health Savings Accounts (the IRS is confused about DPC) 
Medicare/Medicaid/State Employee Pilot Projects