"Is it legal for landlord requiring tenants to pay the rent of remaining period when terminating the contract?"

I signed an 1-year lease contract with current landlord 3 months ago. The agreement stated that when I terminate the contract and move out early, I should pay the rent of remaining period. The landlord told me it is natural to do so I believed what she said. But I later found that most landlords do not require such thing but accepts "early termination fee" instead. Is it legal for landlord requiring tenants to pay the rent of remaining period in case of early termination? If not, I will ask my landlord for lease amendment.