Declining the LSA can only be done if you have not accepted it beforehand (e.g. on your first login, or when a new version of the LSA is released.) However, if you decline the agreement, you will not be able to accept any tasks in Port.
Log in for the first time
Select Profile from the main menu
Your General details will be displayed
Select the Agreement text link
The LSA will be displayed
A message will confirm your action