The "Notice of Acceleration" sometimes called a "Demand Letter," normally states that the whole balance is due and payable immediately. If you fail to pay the entire amount due, the lender has the right to foreclose on the mortgage. However, the lender must comply with the requirements of the loan documents and other relevant laws, so it is important to seek advice from a Housing and Urban Development-approved credit counselor or an attorney as soon as you receive a "notice of acceleration/demand letter."