In Indian polity, withholding relieving letters is brutal. It makes it very hard for the laid-off person to get another job: one must present a relieving letter to be hired elsewhere.
Courts aren't a useful remedy for a worker with a family to feed: too slow and expensive.
You are supposed to get an experience certificate (that confirms how long you worked in that company) and a formal relieving letter (that confirms that you left under normal circumstances and your performance was satisfactory) from your previous employer. In addition to that you are also supposed to get payslips for the last three months.
Without supplying these it is very hard to get a job. Most companies also contact previous employers (through a third party) to confirm these details.
Courts aren't a useful remedy for a worker with a family to feed: too slow and expensive.