Changing the employment contract
Working in Lithuania on the basis of employment contract and after implementation of new Labour Code your employer initiates changes of your Contract saying that it is compulsory?
It is not compulsory UNLESS if new regulations change your working conditions to the better than you have currently.
If employer still wishes to make some changes:
Read new employment contract (or its new Annex) carefully and make sure that new provisions are not worse than previous and you actually agree with them.
If employer changes working conditions and you do not do anything about that 3 months in a row, it is thought that you agreed with the changes and you can not dispute them later.