613 Mitzvot
Negative Mitzvah 48
Not to make covenants with idolators
Devarim (Deuteronomy) 7:1,2
1 Ki yevi'acha YHVH Eloheycha el-ha'arets asher-atah va-shamah lerishtah venashal goyim-rabim mipaneycha haChiti vehaGirgashi veha'Emori vehaKna'ani vehaPrizi vehaChivi vehaYevusi shiv'ah goyim rabim va'atsumim mimeka.
When YHVH your Elohim brings you to the Land, so that you will go to possess it, and you have cleared away many nations before you, the Chiti, and the Girgashi, and the Emori, and the K'na'ani, and the P'rizi and the Chivi, and the Yevusi, seven nations greater and mightier than you.
2 Unetanam YHVH Eloheycha lefaneycha vehikitam hacharem tacharim otam lo-tichrot lahem brit velo techonem.
And when YHVH your Elohim has delivered them before you and you have conquered them, destroying, you shall destroy them. You shall not cut a covenant with them, nor show them pity.

This mitzvah applies specifically to the seven pagan nations of the Land (along with their meanings):

This mitzvah prohibits making covenants with these seven nations that inhabited Eretz-Yisra'el before its conquest by the children of Yisra'el. Even though it applies specifically with Eretz-Yisra'el, there is an universal principle that can be applied by all followers of YHVH. We should not make any agreement with people or organizatons that are contrary to the ways of YHVH.

2 Korinthi 6:14-18
Don't be unequally yoked with unbelievers. For what fellowship has righteousness with lawlessness? And what does light and darkness have in common? And what agreement does Moshiach have with Beliya'al? What part does a believer have with an unbeliever? And what covenant does the Temple of YHVH have with idols? For you are the Temple of the Living Elohim, since Elohim has said, "I will walk among them" (Lev 26:12) and "my Mishkan (Tabernacle) will be among them and I will be their Elohim and they will be my people" (Ezek 37:27). Therefore "Depart and go away from them," says YHVH, "Touch no unclean thing (Is 52:11) and I will receive you (Ezek 20:41). I will be a Father (Abba) to you, and you will be my sons and daughters, says YHVH Tz'vo'at (2 Sam 7:8,14).

This verse is often applied to marriages, but it relates to any type of partnership or contract.

Shemot (Exodus) 23:32-33
You shall make no covenant with them, nor with their elohim. They shall not dwell in your land, lest they make you sin against me, for if you serve their gods, it will surely be a snare to you."

Shemot (Exodus) 34:12-16
Be careful, lest you make a covenant with the inhabitants of the land where you are going, lest it be for a snare in the midst of you: but you shall break down their altars, and dash in pieces their pillars, and you shall cut down their Asherim; for you shall worship no other elohim: for YHVH, whose name is Qanna (Jealous), is a jealous Elohim. Don't make a covenant with the inhabitants of the land, lest they play the prostitute after their elohim, and sacrifice to their elohim, and one call you and you eat of his sacrifice; and you take of their daughters to your sons, and their daughters play the prostitute after their elohim, and make your sons play the prostitute after their elohim.

The main reason that YHVH does not want us to make a covenant with them is that they will draw us into idolatry.

1 Korinthi 15:33
Don't be deceived! "Evil companionships corrupt good morals."

Ya'akov (James) 4:4
You adulterers and adulteresses, don't you know that friendship with the world is enmity with Elohim? Whoever therefore wants to be a friend of the world makes himself an enemy of Elohim.