Economists aren’t sure whether this year’s increases are a one-time phenomenon centered on a small set of big companies or herald a longer-term shift toward higher wages. Japan’s chronic labor shortage and lack of large-scale immigration have heightened the competition to hire talent. 

Hitachi said it would increase wages by an average of 3.9%, including seniority-based increases, the largest raise in a quarter-century and more than last year’s 2.6% increase.

Wednesday was the deadline set by unions for companies to release their wage plans for the coming year, with many companies starting their fiscal year in April. Japanese call this period the spring offensive, a term that dates to the early postwar decades when companies and labor unions often clashed over wages.    

The military metaphor was less fitting this year because many companies simply accepted union requests.

Toyota

TM -0.33%

Motor Corp. and Honda were among them.

Suntory Holdings Ltd. said last week it would raise wages by 7% on average, including seniority-based increases. It said it accepted in full a request from its union to add the equivalent of about $75 to monthly pay across the board.

The Japan Council of Metalworkers’ Unions, whose members include unions at auto makers and electronics makers, said its workers got the biggest raise since it started collecting comparable data in 2014. 

Wage growth has been nearly flat for decades in Japan partly because employees tend to favor job security over higher pay. In economic downturns, Japanese companies generally hesitate to lay off workers or slash wages.

That put workers in a tough position last year when external forces including high oil prices, supply-chain bottlenecks and the war in Ukraine pushed prices up in Japan. Inflation hit 4% late last year. Real wages, which reflect the impact of inflation, fell 4.1% in January compared with a year earlier.

With the wage plans released in recent weeks, employees at big companies are likely getting pay increases enough to roughly cover the higher prices they are paying—a goal laid out by Prime Minister

Fumio Kishida.

Some small companies are doing much less, giving workers less than $10 a month in extra base pay, said

Katahiro Yasukochi,

the head of the Japanese Association of Metal, Machinery and Manufacturing Workers, which represents workers at smaller companies. 

“Unfortunately, these companies do not understand that this year’s spring offensive is an extraordinary one,” he said.

Japan is still recovering from Covid-19 pandemic restrictions, and it was only this Monday that the government said it was acceptable for people to go without masks indoors.

Takayuki Miyajima,

an economist at Sony Financial Group, said a postpandemic recovery in the service sector, which mostly consists of small businesses, could help generate a broader-based move for wage increases.

Write to Megumi Fujikawa at megumi.fujikawa@wsj.com