Checking population by contraceptive methods is another sinful activity.

Formerly people used to beget one hundred to two hundred sons and daughters. At the present moment, no one can produce such huge quantities of children. Instead, mankind is very busy checking the increase of population by contraceptive methods. We do not find in Vedic literature that they ever used contraceptive methods, although they were begetting hundreds of children. Checking population by the contraceptive method is another sinful activity, but in this age of Kali people have become so sinful that they do not care for the resultant reactions of their sinful lives. According to the Vedic scriptures, the contraceptive method should be restraint in sex life. It is not that one should indulge in unrestricted sex life and avoid children by using some method to check pregnancy. If a man is in good consciousness, he consults with his religious wife, and as a result of this consultation, with intelligence, one advances in his ability to estimate the value of life. In other words, if one is fortunate enough to have a good, conscientious wife, he can decide by mutual consultation that human life is meant for advancing in Krishna consciousness and not for begetting a large number of children. Children are called parinama, or by-products, and when one consults his good intelligence he can see that his by-products should be the expansion of his Krishna consciousness.

Source: A.C. Bhaktivedanta Swami Prabhupada (2014 edition), “Srimad Bhagavatam”, Fourth Canto, Chapter 27 – Text 06