From Financial Planning:

Critics had argued that the low $600 threshold would go after shadow economy workers like  housekeepers and contractors, not wealthy Americans.

$600 was “a fine-mesh fishing net designed for minnows to catch whales,” argued Jerry  Theodorou, the director of the finance, insurance and trade program at the R Street Institute, a  nonprofit, free market think tank in Washington, D.C. “It is not clear how the plan will achieve the objective of combating ‘sophisticated evasion’ by collecting information, the vast majority of  which is not directed at the plan’s target.”