The move is the latest by the German sportscar manufacturer as it looks to increase its shareholding in the firm to 75 per cent in 2009, according to reports.
In the past, VW has tried to resist bids made by Porsche, but recently the companies reached an agreement to allow Porsche a bigger stake in the manufacturer, which owns SEAT, Skoda and Audi among others.
However, it is understood Porsche will not have any controlling power in VW, even if it increases its stake to 75 per cent.
The state of Saxony controls 20 per cent of VW and has the power to decide how the company is run. Porsche would need more than 80 per cent of the shares to control the company.
VW also has a dominant shareholding in Swedish truckmaker Scania and under Swedish law, Porsche has to make a takeover offer for that firm too.
However, Porsche is believed not to be interested in Scania and will make an offer for the shares that will see it is unlikely to take control.
Porsche has been steadily increasing its VW shareholding from 42 per cent to the current 50.76 per cent over the past year.
VW shares rose from 210 euros to more than 1,000 euros in October – briefly making the firm the most valuable company in the world.
by Nicola Linnington