TOKYO (AFP) - Japan's upper house of parliament, often called the chamber of wisdom, has been rocked by a dress code row after a minister appeared sporting a red scarf.

Justice Minister Midori Matsushima wore the stole when she attended a plenary session on Wednesday, prompting complaints from opposition lawmakers.

Decades-old rules ban the wearing of hats, coats or scarves in deliberation chambers and committee rooms.

A ruckus over the alleged sartorial miss-step even helped prevent the house from sitting for 20 minutes on Thursday morning, while committee members debated the definition of "scarf".

Viewers who tuned in to NHK coverage expecting to watch lawmakers at work were shown the empty chamber before the broadcaster switched to filler footage of tropical fish swimming around a reef.

Matsushima, a feisty former journalist known for her outspoken traditionalist views, said she had not broken any rules, and was "surprised" that her clothing choice had been called into question.

"A scarf is simply part of my outfit," she told reporters. "It's an ordinary fashion item for an ordinary woman."

The row had particular piquancy for fellow upper house member Antonio Inoki, a strapping former wrestler known for his outsized chin and his trademark red scarf.

Inoki has apparently refrained from wearing his scarf in the chamber in deference to the rules.

Matsushima said there was a distinction between a scarf that might be worn to keep warm - known as "erimaki" or "muffler" in Japanese - and one worn as an adornment.

"They are different from scarves for women's fashion," she said on Thursday.

Matsushima is one of five women promoted to the cabinet last month, an apparent beneficiary of Prime Minister Shinzo Abe's push for a "society in which women shine".

A spokesman for the upper house said the debate on Matsushima's clothing at an executive committee was "one of the reasons" for a 20-minute delay in the start of Thursday's session.

"The committee could not reach a conclusion and agreed to continue discussions," he said, adding the next executive committee meeting was set for Tuesday.

There are 242 parliamentarians in Japan's upper house, all drawing a minimum salary of 21 million yen (S$245,000) a year.