Igros Moshe (O.C. I #109): This that you apologize for disagreeing with me in a halachic issue – this is totally unnecessary. That is because this is the way of Torah that it is necessary to establish the truth. Chas v’shalom to silence one who disagrees with you – whether he is being more lenient or more strict. [While there is a discussion about disagreeing in a formal court session Sanhedrin 36 where the court is deciding on the guilt or innocence…] it is not a problem to disagree with the gadol (greatest scholar) when he is saying something in the course of teaching the material or even if he is making a practical halachic ruling but he is not part of a formal court. We see this in many places in the gemora where students question their teacher’s view. … It is obvious in these cases the rulings were not part of a formal court session. Furthermore it is apparent that there is no one today who has the status of gadol for this law that no one can disagree with him… Therefore even if you consider me to be a gadol – it is permitted to disagree with me and consequently it is required that you express your opinion and there is no need to apologize. Nevertheless regarding the halachic question that was raised, my view -that I wrote that it is prohibited - is the correct one.
Igros Moshe (YD II #45): This that you apologize because you disagree with my reasoning and my position. I don’t know why you think you need to apologize. There is an absolute need for everyone to clarify the truth according to his own understanding whether that is a more lenient or strict position and even if it disagrees with the views of his teacher (rav) and surely those who are not considered his teacher. Look at what I wrote already in greater detail in Igros Moshe O.C. I #109): If you are perhaps apologizing because of possibly expressing yourself disrespectfully, but anyone who knows me knows that I am Thank G-d not concerned with what anyone says against me and surely not the words of a Torah scholar.
