uncompromising

un- +‎ compromising

uncompromising (comparative more uncompromising, superlative most uncompromising)

1. Inflexible and unwilling to negotiate or make concessions.
   • 1959, Georgette Heyer, chapter 1, in The Unknown Ajax:

     But Richmond, his grandfather's darling, after one thoughtful glance cast under his lashes at that uncompromising countenance appeared to lose himself in his own reflections.

   • 2014 November 14, Stephen Halliday, “Scotland 1-0 Republic of Ireland: Maloney the hero”, in The Scotsman‎:

     The visitors, who surprisingly dropped their talismanic record goalscorer Robbie Keane from their starting line-up for a competitive game for the first time in 13 years, adopted a direct and uncompromising approach.

2. Principled.

• See also Thesaurus:obstinate