John Maynard Keynes writes,

So far as employees are concerned, reductions in contributions are more likely to lead to increased expenditure as compared with saving than a reduction in income tax would, and are free from the objection to a reduction in income tax that the wealthier classes would benefit disproportionately. At the same time, the reduction to employers, operating as a mitigation of the costs of production, will come in particularly helpfully in bad times.

This is from a letter written in 1942 to James Meade, who had suggested varying the payroll tax countercyclically. Meade shared the Nobel Prize in 1977.

Thanks to Mario Rizzo for unearthing the correspondence, and thanks to Tyler Cowen for the pointer.