Japanese companies delivered the biggest wage hikes in three decades this year, the nation's largest union said on Wednesday, prompted by labor shortages and an inflationary squeeze on household income.

Workers' monthly pay will rise 5.1% on average this fiscal year, according to a survey of companies conducted since March by union group Rengo, which has about 7 million members.

The outcome of the shuntō — spring labor negotiations — is seen as key for Japan as policymakers try to engineer a stronger and sustainable economic recovery, with higher household income and spending offsetting the drag on consumption from the rising cost of living.