Is agreeing with a contractor to pay 2.5% of the total amount in case of late payment after six months considered usury, and what should I do if he demands an annual increase that I did not agree upon?

It is not permissible to stipulate an increase on a debt in exchange for a delay in payment, as this is explicit usury. The penalty clause is not permissible in contracts where the original obligation is a debt. This condition is legally void, and it is not permissible to pay this increase to the contractor. The contractor must be reminded of the impermissibility of this act and that it is usury. In the event of a dispute, one must resort to the Sharia court or arbitration.