People have been arguing for "equitable pay" since before the word 'postmodernist' ever entered the English lexicon. In general, equitable pay for a job would entail that no two people are paid differently on the basis of certain characteristics we might deem irrelevant (and this basket of characteristics varies depending on who you ask).

Further, economists, political scientists, and philosophers alike have written on the topic of what is equitable in a capitalist economy, and in terms of distributive justice; there are very few people who would define equitability as the mere existence of an agreement between parties, including the legal system (for example, some contracts can and are deemed unconscionable, and selling organs or oneself into slavery are illegal).