At the memorial gathering outside the presidential palace on Saturday, Mr. Kaczynski defended the police action to remove the protesters, even though they had a permit to be there.

“Today we have the first direct attempt to disrupt our ceremonies,” he said. “Those who are here say, ‘We are doing this legally.’ Yes, formally their actions are legal. But what about their goals? Are they legal or permissible? Is it legal to take away someone’s right to pray? It’s all illegal. We need to say it clearly.”

The government was stunned in October when thousands of people — most of them women dressed in black and carrying black umbrellas, the symbol of their movement — took to the streets to protest a proposed law that would have made all abortions illegal. The measure was withdrawn.

Many see this new law to regulate public assemblies as an attempt to stop such movements from spreading. “This is the sort of effort they are most afraid of,” Mr. Smolar said.

But while much of the attention on the new law has focused on its effect on government opponents, Kazimierz Kik, a political scientist at the Polish Academy of Sciences, said the governing party’s real worry may be its own extreme, right-wing supporters attacking opponents on the streets.

“That would be a shambles, and the whole of Europe would cry in outrage,” Mr. Kik said. “This new law is supposed to protect the government from some of its own supporters.”

In competing protests on Tuesday, thousands of pro-government demonstrators waited with Polish flags flying as counterprotesters from the Committee for the Defense of Democracy passed by.