The Gopis Invoke the Threat of Kamsa - ...maybe

Then the gopis employ the diplomatic principle known as bheda (process of dividing) by using rough language to weaken Krsna. The gopis said, "O knower of religious principles (dharma-jna)! You will be acting irreligiously if you steal the wealth of chastity from women and see them naked."

Seeing that it was futile to instill fear of irreligion (adharma) in Krsna, the gopis then resorted to threats to instill fear: "If you do not give our clothing, we will complain to the king (Nanda or Kamsa)."

Krsna said, "O young girls of Vraja! Do you know who has put all these clothes on the branch of the kadamba tree? While herding the cows I saw them from far away and thought, 'Today the kadamba tree is very attractive with colorful flowers and fruits.' To see this astonishing spectacle I came running here and climbed this tree." 

The young girls replied, "They are our clothes."

Krsna: "That cannot be. If they were yours how did they get on this branch high in the tree?"

Gopis: "You have stolen them and put them there."

Krsna: "Are you blaming me? I am the son of King Nanda. Am I am thief? If you doubt me, then just go to Mathura and complain to King Kamsa."

May I suggest that if the gopis had meant to refer to Nanda, they might have been more likely to call him as "your father" than "the king" when speaking to Krishna. I vote for Kamsa as the subject of this verse.

Sridhara: This is the bolder among the gopis speaking. The king they are threatening to speak to may be Nanda, may be Kamsa.

Vamsidhara...says that the gopis realize that Krishna will not be afraid of his father, so they are threatening to tell Kamsa.

BVT [Sanatan Goswami :: Brihad-vaishnava-toshani]: ...All this was already discussed above when the gopis said Krishna’s virtues are praised throughout the cowherd community (verse 14). “We will tell the king.” Here this is to Nanda. But this refers also to the previous verse [This is a little odd, as Sanatan here starts refering back to the previous verse.] where it was said that “We know you are the dear son of Nanda.” The implication is that Krishna will learn through love rather than force. Or, once again, the implied reference to being a cowherd is a veiled insult—you act like this because you only have cows for company. Or, you are praiseworthy only because of your physical appearance, and not because of any virtues you may have. Dharmajna is a sarcastic statement. They really want to say, “You have abandoned righteousness.


Gopala Champu...

[69] Since Krishna remained silent, a secretive smile of amusement on his face, the gopis went on, “If you don’t, we shall tell the king.” [70] With this statement too they only meant to frighten Krishna, who was without fear. They did not in fact intend to tell on him.(31) [71] Moreover, by saying “the king,” they specified neither KaMsa or Nanda, intentionally leaving it ambiguous, thinking, “Let Krishna think of the king of whom he has the most fear.”