IRS Extending the Tax Assessment Period 

Notice of Employment Tax Determination Under IRC § 7436 

If the Commissioner makes a determination of certain employment tax issues (worker classification and/ or section 530 determinations), the Commissioner may send a Notice of Employment Tax Determination Under IRC § 7436 to the taxpayer by certified or registered mail. Certain Service officials are authorized to issue these notices for the Commissioner of Internal Revenue. The notice is not an assessment of tax. It is a proposed liability of employment tax and gives you 90 days (150 days if the notice was addressed to a person outside the United States) to either agree to the proposed liability or file a petition in the United States Tax Court for a redetermination of the issues contained within the notice. Once the notice is issued, the 90 or 150-day period cannot be suspended or extended. Neither can the notice be rescinded once it is issued 

IRS Publication 1035 (TTT 05/25/2021 & 06/01/21)