Is it permissible for the landlord to demand the difference in currency exchange when checks are due, if the exchange rate of the Jordanian Dinar against the Shekel has increased compared to what it was at the time the checks were issued, and is this considered usury (riba)?

If the lease agreement stipulates a deferred rent, then the rent is a debt owed by the tenant, and two matters result from this:

1. It is not permissible to agree beforehand to pay the debt in a currency other than the currency of the debt, because this involves deferred exchange (Sarf), which is usury (Riba). Exchange between different currencies must be done hand-to-hand (simultaneous exchange).

2. It is not permissible to stipulate or request an increase on the debt because it is usury (Riba).

If it was agreed that the rent is in dinars, then the rent remains a debt in dinars, and the tenant pays it in dinars. It is permissible at the time of payment (not before) to agree to pay it in another currency at the rate of the day of payment, based on the Hadith of Ibn Umar: "There is no harm in taking it at the rate of its day, as long as you do not part while there is still something between you."

If it was agreed that the rent is in shekels, then the tenant is obliged to pay it in shekels. The change in the value of the other currency (the dinar) against the shekel is not taken into consideration, because the agreed-upon currency in the contract is the original.

In summary: The decisive factor is the currency agreed upon in the contract, whether it is dinars or shekels. Its equivalent in the other currency does not affect it except at the time of payment.