The demonstration came days after the death of a taxi driver who set himself on a fire in protest against plans to introduce car-pooling service Kakao Mobility, a unit of mobile messenger operator Kakao Corp.

"If the service is implemented, my income will shrink by half. I'll fall into poverty," said driver Yoon Woo-seok, 62, at the rally in front of the National Assembly.

Drivers wearing black headbands and ribbons to mourn their colleague chanted "combat illegal carpool".

Kakao postponed the official launch of its service after the suicide.

"We will have continued consultations with the industry, parliament and the government," the company said.

South Korea has one of the world's highest smartphone penetration rates, but app-based car-hailing services such as U.S.-based Uber [UBER.UL] have not taken off, partly because of strong unions and tight regulations in Asia's fourth-biggest economy.

The protests pose a challenge to the labour-friendly government, which has also pledged to promote new industries to cut reliance on big conglomerates, such as Hyundai and Samsung.

According to a survey in October by pollster Realmeter, more than 50 percent of the public support carpooling.

The taxi strike stranded commuters and disrupted traffic, with some taxis temporarily blocking a road leading to a highway in the central city of Daejeon, according to photos and media reports.

Seoul's taxi operation rate dropped to 50 percent compared to the same day last week, a transport ministry official told Reuters.

Taxi drivers say they already suffer low incomes and long hours.

"My entire family is scraping a living on my tiny income," said another driver, Lee Nam-soo, 67.

He said he earned 80,000 won ($70) to 90,000 won a day.

"There's no way I can survive if Kakao operates."

Taxi associations urged parliament to ban carpooling, while calling for a crackdown on what they say are illegal carpooling services.

The transport law bans the use of personal vehicles for commercial purposes, but allows carpooling services of drivers with riders heading in the same direction during "commuting" hours. Commuting times are not specified by law, causing confusion.

The ruling party has created a task force to try to resolve the dispute.

(Reporting by Heekyong Yang, additional reporting by Hyunjoo Jin and Ju-min Park; Editing by Nick Macfie)

By Heekyong Yang