Russia's only independent polling agency says it may have to close after prosecutors targeted it for 'political activity.'

Levada Center on Monday published a letter from prosecutors who said its polls and publications are "aimed at shaping public opinion on government policy" and demanded it cease publication until it registers as a 'foreign agent' under a law passed last year.

Russia has pushed strongly in recent months to enforce the law, which requires all foreign-funded NGOs that engage in spuriously defined political activities to register as "foreign agents," a term that recalls Soviet-era propaganda casting suspicion on foreigners. The measure is seen as an attempt to restrict Kremlin critics and undermine their credibility.

So far, 44 NGOs have had legal actions brought against them, according to legal aid group Agora.