Assured shorthold contracts in the UK allow landlords to have a break clause enabling them to end the tenancy at six months, but the landlord can choose not to.
From the guardian.co.uk
Berbatov's four-year deal included a one-way clause in United's favour, enabling the club to extend by one year at any time they choose.
From the independent.co.uk
What added a sense of urgency to the mission was a clause in the CBS deal enabling the NCAA to opt out on July 31.