If a company (say company A) do not want any association or merger with another one (say company B), then A can negotiate with B to back off and request them to sell off the shares if any they have.
If B is no mood to listen, they (B) can still go ahead with the take over and it is called a hostile take over. B's success depend upon several factors including its own management's ability, support from Bank's and financial institutions (including those owning the shares of A), how much the share holders of A resist the move and and also the degree of intervention of the respective National Governments.
For example German government try to protect Volkswagen from any take overs.
One German law introduced to protect Volkswagen has to be squashed when European Union moved against it and European court of Justice ruled against that German law which some people called as Volkswagen law.
Volkswagen law is specific to Volkswagen and is aimed to protect VW from take overs.
Under the "Volkswagen law", any share holder in VW could not excercise more than 20% of the voting rights even if there share holding is much bigger.
In 2007, European court of Justice ruled that this German law protecting Volkswagen from take overs is illegal.
Following the Order, Germany scrapped the law. But in 2008, re wrote it in a different way (don't know the legal terms) and introduced revised Volkswagen law. Now removed limits on voting rights but with a new requirement that any important decisions about the company must be passed by more than 80% majority.
The catch is a German state, Lower Saxony is holding 20.1% stake in VW and its impossible for any other share holder to get more than 80% stake.
The fight is still own with German Government and European Union. German Govt has made it very clear that they are going to aggressively defend VW law in European court of Justice.
This law was introduced when Volkswagen was privitised in 1960.
Further to satisfy your curiosity, a brief flash back:
Volkswagen was founded in 1937 by the Nazi trade union as Ordered by Adolf Hitler.
At that time, Germany had only luxury cars and common people were not able to buy a car. So Hitler ordered a project - kdf wagen. Volkswagen was one of the cars under this project.
The first Volkswagen (people's car) was designed by Ferdinand Porsche, founder of Porsche.
Hitler approved Porsche's design and first people's car was born.
During second world war, there were an estimated 15000 slaves working in VW. Company admitted this in 1998 - Not sure whether this was voluntary on the part of VW or after some survivors in filed a case in 1998 for forced labour and demanded restitution.
In 1945, US forces bombed and captured statd des KdF-Wagens (VW township) and handed over to the British.
None of the major auto companies of the world at that time (and they were in America, Britain and France) were interested to take over VW. So in 1948 VW was kept under West German control.
Mercedes was a brand in the Daimler Motoren Gesellschaft (DMG) which began to develop in 1901, after the death of its co-founder, Gottlieb Daimler. It was actually the name of a beautiful girl, the name Mercédès meaning "mercy" in Spanish. A photo of the girl and a brief history of the brand name from the Mercedes-Benz website may be found here.
And if I remember correctly, she also had three brothers, all of them being racing champions. They held various speed records exceeding 100 MPH, way back in 1910 AD.
Slightly off topic but relevant nevertheless (Jeremy Clarkson on the quality of German vs. American cars):
When Daimler-Benz merged with Chrysler, the American engineers realised after a short while that the Germans at Mercedes were paying five times more for their seats than they were. So they sent some Chrysler seats to Stuttgart saying, “Hey guys. We think you’re being overcharged.”
Having spent a few weeks examining the Chrysler seats, the Germans replied, “Nein. Ve zink it is you who are being overcharged.”