unholy alliance

A play on the name of the "Holy Alliance" (a coalition of Russia, Austria, and Prussia formed in 1815), used in 1855 for Western European alliances with the Ottoman Empire against the interests of Russia, Greece, and most of the Balkans.

Later uses were more literally just unholy + alliance, such as the use in the 1912 US Progressive Party platform, which was quoted by Theodore Roosevelt in his autobiography:

"To destroy this invisible Government, to dissolve the unholy alliance between corrupt business and corrupt politics is the first task of the statesmanship of the day."

unholy alliance (uncountable)

1. A coalition among seemingly antagonistic groups, especially if one is religious, for ad hoc or hidden gain. (See examples.)

• strange bedfellows