The Elegant Gift Shop Had Been a Tenant in Meadowvale

The Elegant Gift Shop had been a tenant in Meadowvale Shopping Centre for ten years. The commercial lease contained a term in which all tenants agreed to participate in all Centre promotional activities and to be open for business during the hours which the landlord stipulated as hours of operation for the centre. At the time Elegant entered into the lease, legislation was in place which prohibited the opening of retail establishments on Sundays and statutory holidays.
Recently, the provincial government's legislation was challenged and was found unconstitutional by the courts, thus allowing retail stores to remain open on Sundays and holidays. The manager of Harborvale Centre immediately sent notices to all mall tenants that the Centre would now be open on Sunday and all shops were required to be open for business. The notice referred to the clause in the lease entitling the landlord to require tenants to be open during the hours designated by the landlord as hours of operation.
What issues does this situation present? Discuss the rights of the parties involved.