A Demand Clause is a clause in the mortgage note that allows the lender to demand repayment of the loan balance in full.

A demand clause is better for the lender than a due on sale clause or acceleration clause, because an acceleration clause allows the lender to call the loan if the borrower violates some contractual provision, such as a requirement that the loan must be repaid upon sale of the property and the demand clause allows the lender to demand repayment for any reason.

For example, the lender can compel you to accept a higher rate by intimidating that if you don't agree, the loan will be called.

The lender asking for a demand clause will no doubt renounce any intention of behaving with such conduct.