A wage hike of 30,000 yen would amount to about a 10% increase in base salaries, analysts say, which would be the largest demand on record.

Blue-chip companies are due to offer unionists pay increases on March 13, followed by small firms that tend to follow their bigger rivals and come up with offers around the middle of the year.

Small firms, which employ roughly seven out of 10 Japanese workers, hold the key to spreading wage hikes, with many workers in regional Japan on their payrolls.

The labour talks have attracted attention from policymakers and central bankers who have said sustainable wage and price hikes are a prerequisite for the Bank of Japan to end negative interest rates.

The BOJ has been laying the groundwork to end negative rates by April as major firms have unveiled hefty wage hike offers one after another this year.

Last year major Japanese firms, faced with chronic labour shortages in a fast-ageing population and rising living costs, offered pay hikes of 3.6% - the largest in three decades.

This year, Japan's largest trade unions confederation Reno is seeking wage hikes of at least 5%.

Japan's Nippon Steel union's pay demand reflects the need to attract more workers and improve labour conditions in a strong steel market, union chairman Naomichi Kono said.

"We are aiming to stimulate private consumption and spread ripple effects across Japan," he said in a statement.

Nippon Steel and other steel makers are members of the Japan Federation of Basic Industry Workers' Union, which also includes ship builders, heavy industry machinery, metal processing, aviation and space, representing about 270,000 workers.

($1 = 149.3900 yen)

(Reporting by Tetsushi Kajimoto; Editing by Sonali Paul)

By Tetsushi Kajimoto