Srila Bhaktisiddhanta warns all devotees engaged in broadcasting the Krsna consciousness movement not to speak to the impersonalist Mayavadis who are always determined to oppose such theistic movements. The world is full of atheists and Mayavadis and the political parties of the world take advantage of their philosophies to promote materialism.

The Mayavadis and other atheists do not want Krsna consciousness to develop because it educates people in God consciousness….There is no benefit in feeding a snake milk and bananas as it simply becomes more poisonous. For a similar reason we should not disclose our minds to the serpent Mayavadis and karmis. Such disclosures will never help. It is best to avoid association with them completely and never ask them anything confidential because they cannot give good advice. Nor should we extend invitations to Mayavadis and atheists, nor accept their invitations, for by such intimate intermingling we may become affected by their atheistic mentality (sangat sanjayate kamah). It is the negative injunction in this verse that we should refrain from giving anything to or accepting anything from the Mayavadis and atheists.

Srila Prabhupada — Nectar of Instruction, Text 4 purport