<http://www.federalreserve.gov/boardDocs/Speeches/2000/20000405.htm>
Short of a significant opening up of our borders to more immigration, an increase in employment beyond the growth of the working-age population is limited to what remains of our shrinking pool of available workers. Although the sum of the unemployed and those not in the labor force but who nonetheless are available for work is still about ten million, the level has been falling steadily. This year, the figure has been lower as a percentage of the population than at any time in the history of this series, which goes back to 1970. Should the pool of available workers continue to shrink, there is a point at which this safety valve for excess demand will effectively close, even in the face of accelerating productivity. We do not know where that point is, but presumably it would occur well before a full depletion of the pool of potential workers. When we reach that point, short of a repeal of the law of supply and demand, the scarcity of labor will almost surely induce a rise in hourly compensation gains that increasingly outpaces an even faster productivity growth--a condition that would cause unit costs to accelerate over time.
This was April 2000, as the Nasdaq was peaking. He said this quite a few times starting around 1996. Doug
