Poland has threatened to freeze progress in EU-Belarus relations and to lobby the IMF to cut off aid following a crackdown on ethnic Poles.
Police on Monday (15 February) arrested the leader of the Union of Poles in Belarus, Angelika Borys, along with around 40 other activists on their way to a rally in Valozhyn, in the west of the country.
The sweep follows a raid on the union's headquarters in Grodno last week and a meeting between the Polish and Belarusian foreign ministers in which Warsaw told Minsk to back off.
"Thanks to Polish engagement Belarus has found itself in the Eastern Partnership. Poland would like to continue the trend of gradually developing contacts," Polish deputy foreign minister Andrzej Kramer told press in the Polish capital on Monday.
"But a negative scenario is possible, which would mean the self-isolation of the Belarusian side, if these repressive acts continue."
Mr Kramer said Poland will deny visas to any Belarus officials involved in the events. Warsaw has also asked EU foreign ministers to discuss the situation at a regular meeting in Brussels next week.
The Polish government is in a tricky spot.
On the one hand it is facing public pressure to act tough. But it does not want to jeopardise its strategic aim of bringing Belarus closer to the EU or its efforts to improve the lives of ordinary people living in the authoritarian state.
If the crackdown continues, Poland is likely to try and block any prestigious high-level EU-Belarus meetings.
It may try to halt Belarus' inclusion in EU-funded projects under the Eastern Partnership, a recently-launched policy to boost ties with six post-Soviet states. It could stymie talks on visa facilitation and call for an EU travel ban on senior Belarus officials to be re-activated.
A Polish diplomat also underlined Warsaw's growing influence in the International Monetary Fund (IMF), which is propping up Belarus' crisis-hit economy with billions of dollars in aid. "We will try to exert pressure in all international fora where Poland has a voice," the diplomatic contact said.
The Polish Union in Belarus is the largest independent NGO in the country.
Belarus is home to 400,000 ethnic Poles following a change in borders after World War II, which pushed the Polish frontier to the west.