"History has recorded the development of reformism in all developed capitalist countries. Already Marx and Engels pointed to the social and class roots of opportunism and reformism. For them, reformism is not accidental, the delusion of these or those ideologues, not even an accidental vacillation of these or those strata of the working class. There is a historical regularity of reformism. Its class essence and ultimate goal have a bourgeois character. The basic, prevailing social basis of reformism is the bourgeoisie. Part of the working class that was recruited from proletarianized strata, was connected to it by thousands of threads and ties. In the struggle to create a political party, Marx and Engels led an unwavering and irreconcilable struggle with petty-bourgeois reformism, which appeared in the form of Proudhonism and Lasallianism with reformist ideology, which was created by the labor aristocracy in England and later in the USA. Substantial layers of highly skilled workers in England were created by the high wages paid by the English bourgeoisie at the expense of the exploited colonies and the monopoly profit which it collected using the monopolistic position of England on the world market. In the English trade unions, reformism got its way in ideology and practice. England is, in fact, his cradle. The ideas of the class struggle, the principles of the dictatorship of the proletariat and the socialist revolution were alien to the trade unions. Representing the opinion of not changing the capitalist order, they denied the existence of class contradictions between labor and capital and claimed that neither labor nor capital can exist without each other, and there is not, and cannot be, antagonism between him..."

Written by Josip Cazi (Yugoslav revolutionary and writer) in the book named "From the way of reformism to the way of class struggle". I sadly can't find an English translation (but I plan to translate the book). But here it is for my Serbo-Croatian speaking comrades:

http://radnici.ba/wp-content/uploads/2018/04/S-puta-reformizma-na-put-klasne-borbe-Josip-Cazi.pdf