The ongoing supply shortages that are propping up home prices in many metro areas caused pending home sales in May to slump for the third consecutive month, according to the National Association of Realtors. None of the major regions saw an increase in contract activity last month.

The Pending Home Sales Index, a forward-looking indicator based on contract signings, decreased 0.8 percent to 108.5 in May from a downwardly revised 109.4 in April. The index is now 1.7 percent below a year ago, which marks the second straight annual decline and the most recent since November and December of last year.

Lawrence Yun, NAR chief economist, says it's clear the critically low inventory levels in much of the country somewhat sidetracked the housing market this spring. "Monthly closings have recently been oscillating back and forth, but this third consecutive decline in contract activity implies a possible topping off in sales," he said. "Buyer interest is solid, but there is just not enough supply to satisfy demand. Prospective buyers are being sidelined by both limited choices and home prices that are climbing too fast."