The highly popular biscuit - with its oblong shape, 52 teeth and optional slab of chocolate on one side - has been a favourite in French households since it was first put into production in 1846.
But now its future is in doubt after a string of troubles at the factory in La Haye-Fouassière, near Nantes, where they are produced.
French newspaper Le Figaro reported a decrease in production volumes, from 45,000 tonnes in 2014 to 31,000 tonnes today.
The number of employees has fallen from 500 to 330, according to figures from the trade union CGT, which also warns of the loss of around 15 jobs by 2020.
And this week the factory's troubles intensified with calls for strike action over the dismissal of a long-serving employee.
The American agri-food group Mondelez, which has owned LU since 2007, says the dismissal is due to repeated health and safety breaches, but this has been challenged by union officials, who have spoken of a tense atmosphere at the factory.
The biscuits have been a staple treat for many since childhood since they were first created by Louis Lefèvre-Utile in his parents' biscuit company.
The classic Petit Beurre range was later expanded with the addition of dark or milk chocolate with the figure of the petit ecolier (little schoolboy) that has become the emblem of the brand.