Enforcement of tax collection limited by statutory delay, with dispute and recovery-risk exceptions permitting earlier action. Commissioner may not enforce payment of assessed tax or penalties until two months after service of the notice of assessment, and where a compliant objection has been made the balance in dispute may not be enforced until the Commissioner resolves the objection; however, recovery proceedings may continue for amounts not in dispute or where an appeal has been filed, and the Commissioner may specify an earlier collection date in the notice when satisfied delayed collection risks recovery.