Commentary for Nedarim 55:15

1. For a tax collector that is collecting without limit. This is not law but thievery, and a tax collector's theft is not a law.

2. The tax collector standing over him. "...The Tosafot wrote that the concept of 'dina de-malchuta dina' applies exclusively to non-Jewish Kings; since the land is his and he can say that if one doesn't obey his command, he will expel them from the land; however, Jewish kings may not because all Jews are partners in the Land of Israel" [translation from http://adderabbi.blogspot.com/2005/02/ran-on-nedarim-28a-and-israeli.html]