UPDATE Trigger fired twice?

I have writen the following UPDATE trigger in SQL Server:

CREATE TRIGGER LOG_UPDATE ON EMPLOYEE
AFTER UPDATE
AS
INSERT change_log(table_name,operation,key1)
SELECT 'EMPLOYEE','U',EMP_ID
FROM inserted

I want a record to be inserted in the CHANGE_LOG table when an update occurs at the EMPLOYEE table. But the problem is two records are getting inserted in CHANGE_LOG table instead of one. It seems as if the UPDATE trigger is fired twice. Please suggest a solution.
Thanks,
Vibha