Companies are not free to fire workers solely for the company's convenience. To fire a worker requires sufficient reasons. Firing workers is invalid if it does not fulfill certain conditions, such as punitive dismissal of workers who violate company rules, or ordinary dismissal that is allowed for other reasons.
Even in cases where companies can legally dismiss workers, the companies must give the workers at least one month's notice. If no notice is given, the companies must pay the workers a termination notice allowance.
These restrictions also apply to a certain extent to termination of fixed-term contracts. If a contract has a fixed term but can be renewed indefinitely as long as there are no problems, or if a contract has been renewed for so many years that it is almost the same as a contract without a fixed term, termination of the contract is restricted in the same way as dismissal.
In the case of foreign workers, these restrictions on dismissal and termination of employment are often not followed.
Sometimes workers are dismissed or terminated for no reason other than the convenience of the employer. If you suspect an unfair dismissal or termination of your contract, you should immediately consult with the Migrant Worker Research Group or a labor union.
On the other hand, there are cases in which a worker may request resignation. In the case of a contract with no fixed term, a worker can resign by giving the company two weeks' notice. In the case of a contract with a fixed term, however, the worker cannot, in principle, resign until the end of that term. In this case, the resignation can only be made under unavoidable circumstances.
Some companies claim damages against workers when they quit in the middle of a contract, so be careful when resigning.