In the case of Mempa v. Rhay, Jerry Mempa pleaded guilty to "joyriding" (unauthorized use of vehicles) and was placed on probation for two years. During his probation period, he was involved in a burglary and subsequently arrested. At his hearing regarding revocation of probation, he did not have legal representation nor was it offered to him by the court. His probation was revoked and he received a maximum sentence for both crimes - joyriding and burglary. Mempa appealed this decision arguing that under the Sixth Amendment's guarantee of counsel clause, he should have had an attorney present at his revocation hearing. The Supreme Court agreed with him unanimously ruling that defendants are entitled to legal counsel during every critical stage of their criminal proceedings including sentencing or hearings related to parole or probations violations. This landmark decision expanded upon Gideon v Wainwright which established right-to-counsel in felony trials; now extending it further into post-conviction stages as well ensuring fair treatment throughout entire judicial process.

In the dissenting opinion for Mempa v. Rhay, Justice Harlan argued that the majority's decision to require counsel at every stage of a criminal proceeding was an overextension of the Sixth Amendment right to counsel. He contended that this requirement should only apply when substantial rights could be affected, not in situations like probation revocation hearings where defendants are merely asked about their behavior while on probation. Furthermore, he believed it was unnecessary and impractical to provide legal representation during such proceedings because they were administrative rather than adversarial in nature. This would place an undue burden on states' resources without significantly improving outcomes for defendants.