If you already work for the government, a public sector undertaking or an autonomous body, you cannot simply apply for another post. Most notifications ask for a no-objection certificate (NOC), and missing it can undo a selection.
Employees of central and state governments, PSUs, public sector banks and autonomous bodies, whether permanent, temporary or on probation. Contract staff should check their own agreement.
Some notifications need only a declaration that you have informed your employer in writing; others require the NOC itself at the interview or document verification. The wording is in the general instructions.
That the employer has no objection to your candidature, and usually that no vigilance or disciplinary case is pending.
You will need a relieving order. If the new post is also under government, ask about technical resignation, which can protect past service for pension and leave; an ordinary resignation does not.
If you are under a training bond, the amount may be recoverable or transferable; check before you resign.
Look for the serving-employee clause in each notification under latest government jobs. See also joining and probation.