At stake is the name of the company which sells 40,000 pairs of the no-nonsense shoes every day of the year. Fans include Leonardo DiCaprio, Gwyneth Paltrow and Johnny Depp.
Susanne Papenbrock, 34, is divorcing the firm's heir, Christian Birkenstock, after a 15-year marriage and wants to take the company name with her. Newspapers have dubbed the divorce fight "Dallas on the Rhine".
Ms Papenbrock, who walked out of the River Rhine castle she shared with her husband two years ago, has started a rival company using the Birkenstock name. She markets a sandal called Beautystep that was produced by the "Susanne Birkenstock International" firm and touts her married name in adverts for it. Helped by her blonde good looks the shoe became a hit and she has appeared on numerous German TV talk shows.
Mr Birkenstock, who controls the original company with two brothers, went to court in Cologne to seek an injunction. In their filing they said it was clear "that the defendant's sole mission is to sponge off the reputation of the plaintiff's brands".
The company sales director wrote to major newspapers and retailers accusing Ms Papenbrock of "lying for marketing purposes". He even wrote to Chancellor Gerhard Schrder and members of his cabinet. The letter went on to mention that she received the house where her company was operating from as a gift from her husband.
Mr Birkenstock said he was supportive of his wife's business venture - until she decided to use the family name. He added: "The problem was that retailers were calling, asking: 'What's this new product of yours?'
"We didn't want someone who knows the true Birkenstock to turn around and say: 'What are these funny things?'"
Ms Papenbrock filed an injunction to prevent any more letters being sent, while claiming that Birkenstock, whose image is more hippie than hard, was putting the squeeze on retailers to block her Beautystep shoe. She says she is entitled to the name, having helped "sex up" the image of the shoe that enjoyed a mung-bean-and-goat-cheese reputation before she came along.
Ms Papenbrock said there will be no surrender even though the Cologne court said she had to drop the Birkenstock from her firm's name. She now calls her company SB International, but her adverts still carry her married name, arousing the continued ire of Birkenstock lawyers.
The next battleground will be in the US, where Ms Papenbrock's firm is expanding.