The Moscow headquarters of two influential human rights groups were vandalized on Wednesday, Nov 21, the first day a controversial new law on non-governmental organizations (NGO) took effect, RIA Novosti reported.

The entrances to the offices of Memorial and For Human Rights, two prominent civil rights groups headed by veteran activists, were spray-painted with the words “Foreign Agent,” along with a heart shape next to “USA,” according to photos posted on Memorial’s Facebook page.

A law that took effect on Wednesday requires Russian NGOs working in the political sphere and which receive financing from abroad to register as “foreign agents.” Critics have slammed the move as part of a wider Kremlin crackdown on dissent.

The implementation of the NGO law follows another piece of controversial legislation, signed into law last week by President Vladimir Putin, which broadens the definition of treason.

While lawmakers argue that the law is meant to strengthen state security, critics claim the move is an attempt to further stifle civil society. The bill targets those who offer consultation or financial services to individuals and organizations engaged in “activities directed against the security of Russia.”