Karnataka High Court held that (which is wrongly understood by many) once the advocate of a case on record of the Court is discharged, as per procedure established by law (termination letter and communicating the same to advocate), a party has absolute right to engage another advocate and no need of obtaining a separate NOC from the advocate, who was discharged. This was further clarified by a Division Bench here.

From Paras 6 to 9,

6. As could be seen from the observations made in the two decisions extracted above, a party to a litigation has an absolute right to appoint an advocate of his choice, to terminate his services, and to appoint a new advocate. A party has the freedom to change his advocate any time and for whatever reason. However, fairness demands that the party should inform his advocate already on record, though this is not a condition precedent to appoint a new advocate.
7. There is nothing known as irrevocable vakalatnama. The right of a party to withdraw vakalatnama or authorization given to an advocate is absolute. Hence, a party may discharge his advocate any time, with or without cause by withdrawing his vakalatnama or authorization. On discharging the advocate, the party has the right to have the case file returned to him from the advocate, and any refusal by the advocate to return the file amounts to misconduct under Section 35 of the Advocates Act, 1961. In any proceeding, including civil and criminal, a party has an absolute right to appoint a new Advocate. Under no circumstance, a party can be denied of his right to appoint a new advocate of his choice. Therefore, it follows that any rule or law imposing restriction on the said right can’t be construed as mandatory. Accordingly, Courts, Tribunals or other authorities shall not ask for ‘no objection’ of the advocate already on record, to accept the vakalatnama filed by a new advocate.
8. As observed in the decisions referred to above, if an Advocate is discharged by his client and if he has any genuine claim against his client relating to the fee payable to him, the appropriate course for him is to return the brief and to agitate his claim in an appropriate forum, in accordance with law.
9. As stated above, under no circumstance, a party can be denied of his right to appoint a new advocate of his choice. The right is absolute and not conditional. Hence, the objection raised by the Registry on the vakalatnama is overruled. Hereafter, the Registry shall not ask for ‘no objection’ of the advocate already on record, to accept the vakalatnama filed by a new Advocate.

Citations : [2016 SCC ONLINE KAR 6470], [2017 ILR KAR 59], [2017 AIR KAR 1], [2017 KCCR 1 383], [2017 AIR KANT R 4 210]

Other Sources :

https://indiankanoon.org/doc/128027421/

https://www.casemine.com/judgement/in/5845968353bee765a86aed81

Other Judgements on this subject here.