The foreign ministry urged the Belarusian authorities to stop the "arbitrary persecution" of members of the Polish minority in that country.
Meanwhile, Michał Dworczyk, the Polish prime minister’s chief of staff, said the detention of Andżelika Borys on Tuesday was "a typical example of an attempt to intimidate the Polish community" in Belarus, Poland's eastern neighbour.
Dworczyk added: "We absolutely do not accept the persecution of the Polish minority in Belarus."
Borys was detained by police in the city of Grodno in western Belarus, close to the border with Poland, on Tuesday afternoon, Polish state news agency PAP reported.
On Wednesday, she was sentenced to 15 days of detention for organizing an "illegal mass event", according to PAP.
Borys is the head of the Union of Poles in Belarus, the largest Polish organization in that country.
Andrzej Pisalnik, who is active in the Union, said Borys was detained for organising a traditional fair held by the association every year. This year it took place on March 7.
The Union of Poles in Belarus is not recognized by the Belarusian authorities but is nevertheless active, according to the PAP news agency.
Borys was re-elected as its leader on Saturday.
The foreign ministry in Warsaw said that the Union of Poles in Belarus focuses on cultivating Polish culture and tradition as well as supporting Polish education and Polish language learning.
Arrest 'tantamount to eliminating Polish identity'
It added in a statement that the arrest of Andżelika Borys "is tantamount to eliminating Polish identity and not only deals a blow to the good relations with Poland but also inflicts damage to Belarus’s traditional multiculturalism."
The foreign ministry said that on Tuesday it summoned the chargé d’affaires of the Belarusian embassy in Poland, who "received a clear message that the actions taken by Belarusian authorities are contrary to that country’s international obligations to protect national minorities as well as Polish-Belarusian bilateral commitments to protect the Polish national minority."