Continuing our discussion regarding oaths under duress, our gemara on amud aleph questions why dodging tax collectors is a valid situation of duress. There is a teaching that דִּינָא דְמַלְכוּתָא דִּינָא The law of the kingdom is the law, i.e., there is a halakhic principle that Jews must obey the laws of the state in which they live.

This halakhic rationale and degree to which the law of the secular government is binding, is subject to debate amongst poskim. Some see the reach of the secular government extends only to monetary matters, and even so possibly only when not explicitly against Torah law (see discussion in Shach CM 73:39).  There also may be a deeper concept, closer to the notion of Divine Right. That is, the king or possibly the Kingdom and government can make laws that are relevant to enforcing its scope and authority (see Responsum of Rashba 3:109, Chidushei Rashba Bava Basra 55,  Beis Yosef CM 26 and Darchei Moshe CM 369.)  Rashba seems to suggest a secular king has the authority of all that is stated in the warning about Kings (Shmuel I:8:11-17 and Gemara Sanhedrin 20b), which is quite broad and beyond monetary matters. Ironically, a Jewish king may be bound by halakha and more limited in the scope of what he can appropriate for his purposes (see Ran Nedarim 28, Rashba and Tosafos.)

There is an interesting Yismach Moshe (Shemos 5), that reads a halakhic discussion about Dina Demalchusa into the interchange between the Jewish midwives and Pharaoh.  (Another example of the Midrashic Genre of reading lomdus into Biblical protagonists, see Psychology of the Daf, Yevamos 96):

As we know, Pharaoh decrees that the Jewish midwives should murder all the male children born, so as to make it appear that they died in childbirth.  The midwives bravely refuse to “follow orders” (Shemos 1:15-19):

וַיֹּ֙אמֶר֙ מֶ֣לֶךְ מִצְרַ֔יִם לַֽמְיַלְּדֹ֖ת הָֽעִבְרִיֹּ֑ת אֲשֶׁ֨ר שֵׁ֤ם הָֽאַחַת֙ שִׁפְרָ֔ה וְשֵׁ֥ם הַשֵּׁנִ֖ית פּוּעָֽה׃ 

The king of Egypt spoke to the Hebrew midwives, one of whom was named Shiphrah and the other Puah,

וַיֹּ֗אמֶר בְּיַלֶּדְכֶן֙ אֶת־הָֽעִבְרִיּ֔וֹת וּרְאִיתֶ֖ן עַל־הָאָבְנָ֑יִם אִם־בֵּ֥ן הוּא֙ וַהֲמִתֶּ֣ן אֹת֔וֹ וְאִם־בַּ֥ת הִ֖יא וָחָֽיָה׃ saying, 

“When you deliver the Hebrew women, look at the birthstool. If it is a boy, kill him; if it is a girl, let her live.”

וַתִּירֶ֤אןָ הַֽמְיַלְּדֹת֙ אֶת־הָ֣אֱלֹקְים וְלֹ֣א עָשׂ֔וּ כַּאֲשֶׁ֛ר דִּבֶּ֥ר אֲלֵיהֶ֖ן מֶ֣לֶךְ מִצְרָ֑יִם וַתְּחַיֶּ֖יןָ אֶת־הַיְלָדִֽים׃ 

The midwives, fearing God, did not do as the king of Egypt had told them; they let the boys live.

וַיִּקְרָ֤א מֶֽלֶךְ־מִצְרַ֙יִם֙ לַֽמְיַלְּדֹ֔ת וַיֹּ֣אמֶר לָהֶ֔ן מַדּ֥וּעַ עֲשִׂיתֶ֖ן הַדָּבָ֣ר הַזֶּ֑ה וַתְּחַיֶּ֖יןָ אֶת־הַיְלָדִֽים׃ 

So the king of Egypt summoned the midwives and said to them, “Why have you done this thing, letting the boys live?”

וַתֹּאמַ֤רְןָ הַֽמְיַלְּדֹת֙ אֶל־פַּרְעֹ֔ה כִּ֣י לֹ֧א כַנָּשִׁ֛ים הַמִּצְרִיֹּ֖ת הָֽעִבְרִיֹּ֑ת כִּֽי־חָי֣וֹת הֵ֔נָּה בְּטֶ֨רֶם תָּב֧וֹא אֲלֵהֶ֛ן הַמְיַלֶּ֖דֶת וְיָלָֽדוּ׃ 

The midwives said to Pharaoh, “Because the Hebrew women are not like the Egyptian women: they are vigorous. Before the midwife can come to them, they have given birth.”

Chida notes two scriptural anomalies: (1) First Pharaoh is referred to as the king of Egypt, and second, he is just called by his name, Pharaoh.  (2) There is verbosity in their excuse, “the Hebrew women are not like the Egyptian women: they are vigorous. Before the midwife can come to them, they have given birth.”  Why compare to Egyptian women?  Why not just say, “The Jewish women give birth vigorously by themselves”?

The midwives were making a halakhic argument to Pharaoh.  “This decree is not for the sake of societal function and cohesion, and therefore you are not acting as authorized.  You are a rogue king.  The proof is that you have made this decree against Jews alone, and not Egyptians (point number 2 above), and therefore we respond to you as a regular citizen and not a king (point number one.)”

In response to this, Pharaoh expands his decree to include Egyptians as well. This is why the verse (1:22) states a new decree, (note the phrase “All his people” and see Rashi Op. Cit.)

וַיְצַ֣ו פַּרְעֹ֔ה לְכָל־עַמּ֖וֹ לֵאמֹ֑ר כָּל־הַבֵּ֣ן הַיִּלּ֗וֹד הַיְאֹ֙רָה֙ תַּשְׁלִיכֻ֔הוּ וְכָל־הַבַּ֖ת תְּחַיּֽוּן׃ 

Then Pharaoh charged all his people, saying, “Every boy that is born you shall throw into the Nile, but let every girl live.”

However, even though Pharaoh used a legalism, his motives were discriminatory and designed to target the Jews. Therefore, Chida says, the verse wryly notes that this is a ruse, and continues to call him Pharaoh and not King.