(Recasts, adds analyst comment)
By Birsen Altayli and Daren Butler
ISTANBUL, May 18 (Reuters) - Turkish automaker Tofas halted production at its main factory on Monday, as a protest against working conditions intensified and threatened to embarrass President Tayyip Erdogan and the ruling AK Party weeks before a parliamentary election.
Erdogan and the socially conservative, pro-business party he founded are widely credited with guiding Turkey through years of rapid expansion. But that reputation may be coming unstuck as growth slows and unemployment remains above 11 percent.
The protest started on Thursday at Turkey's largest car factory, a plant in the northwestern city of Bursa run by Oyak Renault, a joint venture between France's Renault and the Turkish army pension fund.
On Friday it spread to the neighbouring Tofas plant. Tofas, owned by Italy's Fiat and local conglomerate Koc Holding, said it had halted production until the labour action was resolved, adding it did not expect the stoppage to affect sales.
Together the two automakers account for more than 40 percent of Turkey's annual car output, according to industry data.
Union officials have said the actions amount to protests, but stopped short of formally declaring strikes.
An Oyak Renault spokesman, who asked not to be identified by name, told Reuters late on Sunday that the protest had reached a point where it posed "a serious danger" to the auto sector.
He said talks on resolving the dispute continued between the Turkish Metal Industries Employers' Association and manufacturers in the sector.
It also highlights what critics call one of the contradictions of Turkey's economic progress - that years of rapid growth have not been accompanied by a significant improvement in working conditions.
Around 40 percent of Turkish employees work 50 or more hours a week, the highest among the more than 30 countries in the Organisation for Economic Co-operation and Development (OECD).
An improvement in working conditions is necessary for Turkey to move toward a more European-style society, said Halil Karaveli, an academic and the managing editor of The Turkey Analyst.
"Turkey is second only to China when it comes to work-related accidents. You have an environment where businesses also have to make concessions to labour."
For years the Islamist-rooted AK Party have stayed in power thanks to the backing of the pious working classes, who feel they were shut out of society under decades of secular rule.
Erdogan is hoping for a sweeping victory for the AK Party in June 7 elections, to give it enough votes to push through a constitutional change and hand him broad executive powers.
Shares in Tofas fell more than 4 percent in early trade in Istanbul. By 1115 GMT they were down 1.4 percent. (Writing by David Dolan; Editing by Sophie Walker)