|Those who violate the ban could face up to seven days in jail [EPA]
Belgium has joined France as the second European Union nation to ban people from wearing a full face veil in public.
The ban came into force in Belgium on Saturday, with offenders facing a fine of $197 and up to seven days in jail.
The law, which prohibits people from wearing anything that hides their face in public places, was approved unanimously by parliament in April.
France, home to Europe's biggest Muslim population, became the first EU country to ban full face veils on April 11.
In France, a person who repeatedly insists on appearing veiled in public can be fined $215 and ordered to attend re-education classes.
The law in Belgium faced an immediate court challenge from two women who wear the full face veil, who decided on Friday to challenge the ban in the country's constitutional court, the country's media reported.
"We consider the law as a disproportionate intrusion into fundamental rights such as the freedom of religion and expression," Ines Wouters, the women's lawyer, was quoted as saying in the newspaper La Libre.
"This measure is discriminatory," Wouters said.
The Council of Europe's human rights commissioner, Thomas Hammarberg, criticised such bans this week, saying such measures threaten to exclude women rather than liberating them.
"In fact, the banning may run counter to European human rights standards, in particular the right to respect for one's private life and personal identity," he said.
"The way the dress of a small number of women has been portrayed as a key problem requiring urgent discussion and legislation is a sad capitulation to the prejudices of the xenophobes."