Tomorrow, Fiat CEO Sergio Marchionne will meet with GM boss Rick Wagoner in a showdown meeting that will decide the future of the infamous 'put' option.

As the pressure builds, Marchionne has met the Agnelli family, Fiat's largest shareholder group, today, to brief them on his impending strategy.

Marchionne, unlike his predecessors, has considered a future for the Fiat Group without its carmaking arm, repeatedly commenting in public that his aim is to increase shareholder value.

As he continues to raise the stakes ahead of tomorrow's meeting, which is being held in Zurich on the sidelines of quarterly a Powertrain 'steering committee' gathering, he has reiterated that exercising the 'put' option was a "real live possibility".

GM, saddled with their own restructuring issues, forced upon them by a disastrous downturn in fortunes from their European arm, Adam Opel, want no further role within Fiat's future structure.

After purchasing 20 percent of Fiat Auto four years ago, with a clause inserted to force them to acquire the remaining 80 percent if Fiat so wished it, the infamous 'put' option, a recapitalisation last year has diluted GM's stake down to just 10 percent.

Last week Marchionne told the New York Times, "At the time that Fiat signed all these documents, there was a very clear view that one possible, and a likely outcome, would have been a merger of the auto business with General Motors."

"We cannot change that now because the markets have changed and the economies are not doing as well as one would have hoped," Marchionne concluded, as he continued to build pressure up ahead of this week's meeting. In fact, a year long jointly agreed cessation in hostilities over the 'put' option expires on Wednesday, making the timing of tomorrow's meeting all the more ironic.

GM argue that the structure of the company has since changed, rendering he option invalid, and cite in particular, last year's partial sale of Fidis, Fiat's profitable finance arm. However, Fiat have retained a 'call' option allowing them to by-back this stake, and, are rumoured to be considering whether to exercise this option.

It is believed that GM, anxious also, to avoid longer term Fiat shareholder liabilities, will seek a financial settlement to escape the 'put' option. It is thought that the American carmaker has offered a payment of around 500 million euros, although Fiat are believed to be holding out for close to one billion.

Fiat's close tie-in to GM in the area of joint ventures will also be under discussion. The two companies jointly own Powertrain, a business which has been seeking cost saving rational in the areas of purchasing and engineering development.

Fiat are keen to loosen the tight remit under which it was set up, allowing them to forge new relationships with other manufacturers, something they are currently prevented from doing. "We need to have our strategic freedom back," Marchionne said recently.

Although Powertrain has allowed Fiat to make substantial and vital cost savings, Marchionne is concerned that the joint venture is unable to move quickly enough, an issue of importance to the Italian firm as they seek to speed up the introduction of an array of new models.

Several recent arrivals on the market have been an instant hit, including the new Panda, which in its first year of production is expected to hit around 250,000 units, 25 percent up on its initial targets, and the Ypsilon, which is driving the Lancia brand's revival. Fiat need to build on these success stories, and with a raft of new models scheduled to arrive over the next few year's, including the next-generation Punto in 2005, they want to see development time slashed.

However it's unlikely that Fiat would seek extract itself from the Powertrain venture even if it wanted to, particularly as most forthcoming model development will involve joint platforms and many mechanical programmes have now been integrated.

In Fiat's favour it the fact that GM also need joint ventures in Europe as much as Fiat as they seek to cut their own costs. GM Vice-Chairman Bob Lutz has recently stated that the joint ventures "more than justified the amount of capital that we put in."

Marchionne and senior Fiat managers met with members of the Agnelli family today, the shareholder group who control the Italian carmaker's fortunes. With the influence of Gianni Agnelli having now gone, the reaction of the remaining family to the once-unthinkable idea of selling the car arm is unknown, although they have recently shown their hand by strengthening their grip on the board with the appointment of Gianni's grandsons, John and Lapo Elkann.

Meanwhile some workers at the giant Mirafiori factory in Turin walked out for two hours this afternoon, as the unions, very concerned over the 105-year-old carmaker's future if a sale to GM goes ahead, continue to exert pressure. The unions are calling for Italian Prime Minister Silvio Berlusconi to intervene directly.