The interior ministry had announced a trial period for the weapons at some police districts to assess whether they should become a standard tool for Belgian law enforcement.
"As there is no legal framework, the police officer is individually responsible for using this new weapon," police union VSOA said in a statement.
"(The ministry) has also forgotten to carry out a mandatory risk analysis which is necessary when introducing a new weapon," it added, according to Reuters.
The union announced a strike but did not specify when it would start or which areas would be affected.
Tasers, used by police officers around the world, have been criticized by advocacy groups like Amnesty International and the American Civil Liberties Union, which argue they can be lethal and have called for more stringent rules on their use.