Renault Samsung Motors, the South Korean unit of French automaker Renault S.A., carried out a price hike of up to 750,000 won ($653) across six models without officially notifying customers, according to local reports Sunday.

A total of six models -- the SM3, SM5, SM6, SM7, QM3 and QM6 -- underwent a price increase in line with the release of 2017 model-year vehicles, Yonhap News Agency reported. The firm increased the prices of the popular LE and RE trims of its flagship midsize sedan SM6 by up to 600,000 won earlier this month.

Without sending out customer notifications, the carmaker had slightly changed prices on its website, according to Yonhap.

The price of the popular midsize SUV QM6 released last August also rose between 300,000 won and 350,000 won.

Most trims of the compact SUV QM3 rose by 250,000 won, with the exception of the signature RE trim.

According a Renault Samsung official, the price hike was inevitable and was due to a price increase of raw materials and steel sheets supplied by Posco. The carmaker is not obliged by law to notify price changes for new model-year vehicles.

“Usually companies do not share a press release regarding a price change of new model-year vehicles,” said a public relations representative at the carmaker.

To make up for the price hikes, the auto firm added more options -- such as a soundproof windshield and a light-emitting diode daytime running light -- to regular models.

Observers, however, suggested that Renault Samsung did not announce the price change as it was mindful of Hyundai Motor’s decision to offer the latest version of its Sonata, a midsize sedan that rivals the SM6, at similar or lower prices than previous models.

The SM6 has a price range of 24.2 million won to 32.6 million won, which is about 2 million won more expensive than the new Sonata priced between 22.55 million won and 32.53 million won.

The news reports came amid the carmaker enjoying the biggest growth among local automakers.

It sold 8,008 units in the local market and exported 12,574 units, up 34.3 percent on-year in February, the company said.

The sales hike was led by the SM6 that sold 3,900 units, which is more than 12 times the number sold last year. 

By Kim Bo-gyung (lisakim425@heraldcorp.com)