In the absence of official internal regulations prohibiting what employees can wear to work, the court suggested, Muslim women have a stronger case for wearing the hijab to the office.
The European Court of Justice ruled on Tuesday that employers have the right to ban the wearing of Islamic headscarves in the workplace, on the basis of maintaining religious neutrality.
She claimed she was being directly discriminated against on the grounds of her religion and Belgium's Court of Cassation referred the case to the EU's top court for clarification.
It is the court's first decision on the issue of Islamic headscarves at work.
In 2009, French company Micropole similarly fired Asma Bougnaoui, who had worked as a design engineer since 2008, after a customer complained about her hijab.
Achbita, who worked for the Belgian company G4S, alleged she had chose to start wearing her headscarf after working there for three years and was sacked for violating a company rule.
In France, Asma Bougnaoui was sacked from an IT company after a client requested she remove her headscarf while on their premises. While the cases considered by the ECJ involve the headscarf, the ruling will also apply to other religious symbols such as Sikh turbans, Christian crucifixes, or Jewish Kippahs.
It said: "an employer's desire to project an image of neutrality towards both its public and private sector customers is legitimate" - but national courts had to make sure this policy of neutrality was applied equally to all employees.
Users pointed out that the ruling would disproportionately affect Muslim women.
Women look at veils on display at an exhibition hall during the Muslim World Fair in Le Bourget, France, on Dec.17, 2011.
Employers may bar staff from wearing visible religious symbols, the court ruled.
Amnesty International said the rulings were "disappointing".
In Belgium, there are no federal rules on religious symbols at work, but the regional parliaments have taken measure to prohibit religious, political or philosophical symbols for public service workers who deal with the public.
In Achbita, the European Court held that, as long as the rules are applied consistently across the board, a rule requiring staff to dress neutrally can not constitute direct discrimination.
As a strong anti-immigrant sentiment spreads into the political mainstream and right-wing parties soar in popularity ahead of several key elections this year, the ruling is bound to fan the flames of the long-simmering culture wars across the continent and especially in France. The Court stated that this customer demand was not sufficient to rule out a specific act of discrimination by the employer, and such a demand was therefore directly discriminatory.
The EU court said European Union law bars discrimination on religious grounds, but G4S's actions were based on treating all employees the same, meaning no one person was singled out.
However it ruled that the company must have a policy that bars religious signals and requires employees to "dress neutrally".