Four years ago, Seigo Kawaguchi, a high school gym teacher, stayed sitting at a school graduation ceremony when the Japanese national anthem was played. He was not the only one: most other teachers did too, as did more than 150 students and their parents. Most, to be honest, probably sat out of boredom. But some, including Kawaguchi, felt they couldn't ever stand for a song associated with Japan's military past.

It was an innocuous event, but within two weeks the incident was reported in a rightwing newspaper and the school was bombarded with calls telling the teachers to "go back to North Korea". Kawaguchi was given a written warning, and as a result was inadvertently pushed to the forefront of one of Japan's longest-running and most bizarre legal rows.

Since 2003, more than 500 teachers have been disciplined for refusing to stand and sing Kimigayo - a solemn song about Japan's emperor, which calls for his reign to last "8,000 generations … until the pebbles grow into boulders lush with moss". Standing for it at ceremonies is a requirement in both Tokyo and Osaka.

Some teachers have just been given warnings; others effectively sacked. Appeals have reached the country's supreme court twice, but new cases keep coming. On Thursday morning Kawaguchi went to a high court in Osaka to try and get his warning overturned, saying the requirement restricts his freedom of thought. He lost. He'll now take his challenge to the supreme court.

The issue may seem minor, but the fact that teachers are being asked to stand and sing an anthem at all is a worrying sign of Japan's continued conservatism and desire to please nationalists. There are few other developed countries that have regulations requiring people to stand and sing, and none others that actually enforce the requirement like Japan does.