Russian President Vladimir Putin on Saturday signed into law a new measure that requires non-governmental groups receiving funding from abroad and engaging in political activity to register as foreign agents, The Associated Press reports.

The law also requires NGOs identified as foreign agents to submit detailed annual financial reports, which critics say would be a time-consuming and costly burden on organizations with small staffs and meager funding.

Some NGOs have vowed to ignore or circumvent the law, while its critics note that the vague definition of political activity could be applied against a wide range of initiatives.

The law comes as authorities show increasing unease with a newly emboldened political opposition, which conducted the unprecedented wave of massive public protests in the winter and spring.