ISTANBUL—Turkish automotive workers brought production at two of the country's largest plants to a halt Monday, demanding higher wages as a walkout that started in a Renault SA factory last week spread to Tofas—the local maker of Fiat vehicles.

The protests at the plants in Bursa, south of Istanbul, started at Renault's biggest plant outside Western Europe when workers on the first shift Friday downed tools. On Monday, Tofas Turk Otomobil Fabrikasi AS—manufacturer of Fiat, Citroën, Peugeot, Opel and Vauxhall vehicles—said it was also affected.

"Labor actions that have occurred in a couple of companies operating in the automotive sector in Bursa have been effective on some workers in our factory," Tofas said in a statement to the stock exchange. The company said it decided to stop production until the dispute is resolved.

Fiat Chrysler Automobiles NV declined to comment. A spokeswoman for Renault said the stoppage is illegal and the company wouldn't negotiate with the workers, citing a three-year collective bargaining agreement.

Tofas shares slumped 1.1% to 17.9 liras ($6.9) by Monday noon trading as manufacturing halted, easing from a record high 18.7 liras on Friday to a four-day low as the benchmark BIST-100 Stock Index remained flat. Oyak Renault, which runs the Bursa plant and is a joint venture of the French auto maker and the Turkish army's pension fund, isn't public.

"We see these developments as a one-off that won't have long-term impact on the firm and its stock," said Mehmet Gerz, a portfolio manager at Istanbul-based Ata Invest, which oversees 600 million liras of Turkish assets, including Tofas stock. Tofas's Fiat-Chrysler partnership is opening up previously inaccessible U.S. markets to the Turkish manufacturer, while a new, locally designed passenger auto shows that the "company is on the right road," he said.

The labor walkout, which doesn't officially qualify as a strike, comes on the heels of record vehicle sales in Turkey and rising exports. April auto purchases nearly doubled from last year and are up 56% compared with the 10-year average, while exports jumped 17%, according to data from trade associations.

Workers may be seeking to capitalize on booming sales ahead of the June parliamentary elections, as politicians campaign to raise the minimum wage amid persistently high inflation, analysts said.

The automotive sector provides more than 10% of Turkey's annual exports, and is a key industry for the government as it seeks to turn around sagging economic growth. Oyak Renault produced more than 318,000 vehicles last year, exporting about 81%.

The protests gripped Bursa after the Turkish Metal Trade Union negotiated a 60% raise for employees at a Bosch Ltd. plant in Bursa, prompting union workers at Renault, and then Tofas, to demand similar wage increases. Work-stoppages spread to other Turkish auto-parts manufacturers, according to unions.

"We're faced with a previously unforeseen stance at the Oyak Renault automotive factory in Bursa," the Turkish-French joint venture said Friday. "This stance is not in accordance with current labor laws."

Oyak Renault representatives couldn't be reached for comment Monday, as some 2,500 continued their protests at the factory. A spokeswoman for the French auto maker said: "We're hoping we can try to resolve this calmly."

Turkish Employers' Association of Metal Industries, which represents many companies including Oyak Renault and Tofas, said there would be no changes to Renault's three-year collective labor agreement. The union called for an end to the "illegal" protest.

While declining to comment on the legality of the protest, the Turkish Metal Chairman Pevrul Kavrak called on the workers to resume work. Turkish Metal has 180,000 members nationwide, with 50,000 workers in Bursa, of whom about 20% are participating in the protests.

"End this before it's too late so that we can resolve the matter," Mr. Kavrak said Sunday.

The agreement signed between Turkish Metal and the employees' union on Dec. 15, 2014, runs through the end of August 2017. Renault employees make 9.83 liras an hour, which Turkish Metal says is higher than what the union secured for Bosch workers, whose hourly wage rose to 9.46 liras after no increases for more than three years.

Still, workers estimated in the thousands resigned from Turkish Metal, seeking to force negotiations for higher wages and threatening a prolonged manufacturing-halt barring a new settlement.

Jason Chow in Paris and Eric Sylvers in Milan contributed to this article.

Write to Emre Peker at emre.peker@wsj.com

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