In that essay Krugman treats wage and working conditions as interchangeable, and I think that's the right approach. Two different jobs with different wages can

In that essay Krugman treats wage and working conditions as interchangeable, and I think that's the right approach. Two different jobs with different wages can be equally desirable if one has better working conditions than the other. So to say "Apple should pay more" vs "Apple should have better working conditions" is the same statement, there's no meaningful distinction. Either way the workers would benefit at the company's expense, and the tradeoff between working for, say, Apple vs what the best job there was before Apple built the factory is the same.