Reuters Newsagency says that the falling sales is forcing Porsche to consider cutting production later this year at its main Zuffenhausen plant near Stuttgart where the 911 Carrera is built.
"We have to think about this if car sales continue to develop like this and do not recover," Reuters quoted a company source as saying.
Due to the ramp-up of production of the newly introduced Panamera luxury sedan in the second half of 2009, Porsche's plant in Leipzig, Germany, which assembles the Panamera, and the Cayenne SUV should remain unaffected by the output cuts in Zuffenhausen.
To counteract a severe slump in demand, Porsche said late in January it will cut costs this year by far more than 100 million euros (US$140.7 million) and will halt production in Zuffenhausen by another 19 days before its summer break in addition to the 11 already taken since the start of last December.
A Porsche spokesman said no decision was made yet for further production cuts, but if it became necessary management and labour could decide quickly on such a measure.
In the first nine months of the fiscal year to July, Porsche's global sales fell 28 per cent to 53,635 vehicles.