British Prime Minister Theresa May says if politicians reject her Brexit deal, it will set the country on “a path of deep and grave uncertainty,” AP reported.

Defiant in the face of mounting criticism, May said Thursday she believed “with every fiber of my being” that the deal her government struck with the European Union was the right one.

Two Cabinet ministers have resigned in the 24 hours since the government backed the deal announced Tuesday. An increasing number of lawmakers from May’s Conservative Party are calling for a no-confidence vote on the prime minister.

She told reporters she isn’t planning to give up and would resist a leadership challenge, saying “Am I going to see this through? Yes.”