copied from:
http://forums.catholic.com/showthread.php?t=515033&page=4

Gen 1:28, 9:1,7; 35:11 - from the beginning, the Lord commands us to be fruitful ("fertile") and multiply. A husband and wife fulfill God's plan for marriage in the bringing forth of new life, for God is life itself.
Gen. 28:3 - Isaac's prayer over Jacob shows that fertility and procreation are considered blessings from God.
Gen. 38:8-10 - Onan is killed by God for practicing contraception (in this case, withdrawal) and spilling his semen on the ground.
Gen. 38:11-26 - Judah, like Onan, also rejected God's command to keep up the family lineage, but he was not killed.
Deut. 25:7-10 - the penalty for refusing to keep up a family lineage is not death, like Onan received. Onan was killed for wasting seed.
Gen. 38:9 - also, the author's usage of the graphic word "seed," which is very uncharacteristic for Hebrew writing, further highlights the reason for Onan's death.
Exodus 23:25-26; Deut. 7:13-14 - God promises blessings which include no miscarriages or barrenness. Children are blessings from God, and married couples must always be open to God's plan for new life with every act of marital intimacy.
Lev.18:22-23;20:13 - wasting seed with non-generative sexual acts warrants death. Many Protestant churches, which have all strayed from the Catholic Church, reject this fundamental truth (few Protestants and Catholics realize that contraception was condemned by all of Christianity - and other religions - until the Anglican church permitted it in certain cases at the Lambeth conference in 1930. This opened the floodgates of error).
Lev. 21:17,20 - crushed testicles are called a defect and a blemish before God. God reveals that deliberate sterilization and any other methods which prevent conception are intrinsically evil.
Deut. 23:1 - whoever has crushed testicles or is castrated cannot enter the assembly. Contraception is objectively sinful and contrary, not only to God's Revelation, but the moral and natural law.
Deut. 25:11-12 - there is punishment for potential damage to the testicles, for such damage puts new life at risk. It, of course, follows that vasectomies, which are done with willful consent, are gravely contrary to the natural law.
1 Chron. 25:5 - God exalts His people by blessing them with many children. When married couples contracept, they are declaring "not your will God, but my will be done."
Psalm 127:3-5 - children are a gift of favor from God and blessed is a full quiver. Married couples must always be open to God's precious gift of life. Contraception, which shows a disregard for human life, has lead to the great evils of abortion, euthanasia, and infanticide.
Hosea 9:11; Jer. 18:21 - God punishes Israel by preventing pregnancy. Contraception is a curse, and married couples who use contraception are putting themselves under the same curse.
Mal. 2:14 - marriage is not a contract (which is a mere exchange of property or services). It is a covenant, which means a supernatural exchange of persons. Just as God is three in one, so are a husband and wife, who become one flesh and bring forth new life, three in one. Marital love is a reflection of the Blessed Trinity.
Mal. 2:15 - What does God desire? Godly offspring. What is contraception? A deliberate act against God's will. With contraception, a couple declares, "God may want an eternal being created with our union, but we say no." Contraception is a grave act of selfishness.
Matt. 19:5-6 - Jesus said a husband and wife shall become one. They are no longer two, but one, just as God is three persons, yet one. The expression of authentic marital love reintegrates our bodies and souls to God, and restores us to our original virginal state (perfect integration of body and soul) before God.
Matt. 19:6; Eph. 5:31 - contraception prevents God's ability to "join" together. Just as Christ's love for the Church is selfless and sacrificial, and a husband and wife reflect this union, so a husband and wife's love for each other must also be selfless and sacrificial. This means being open to new life.
Acts 5:1-11 - Ananias and Sapphira were slain because they withheld part of a gift. Fertility is a gift from God and cannot be withheld.
Rom.1:26-27 - sexual acts without the possibility of procreation is sinful. Self-giving love is life-giving love, or the love is a lie. The unitive and procreative elements of marital love can never be divided, or the marital love is also divided, and God is left out of the marriage.

1 Cor. 7:5 - this verse supports the practice of natural family planning ("NFP"). Married couples should not refuse each other except perhaps by agreement for a season, naturally.
Gal. 6:7-8 - God is not mocked for what a man sows. If to the flesh, corruption. If to the Spirit, eternal life.
Eph. 5:25 - Paul instructs husbands to love their wives as Christ loved the Church, by giving his entire body to her and holding nothing back. With contraception, husbands tell their wives, I love you except your fertility, and you can have me except for my fertility. This love is a lie because it is self-centered, and not self-giving and life-giving.
Eph. 5:29-31; Phil. 3:2 - mutilating the flesh (e.g., surgery to prevent conception) is gravely sinful. Many Protestant churches reject this most basic moral truth.
1 Tim. 2:15 - childbearing is considered a "work" through which women may be saved by God's grace.
Rev. 9:21; 21:8; 22:15; Gal. 5:20 - these verses mention the word "sorcery." The Greek word is "pharmakeia" which includes abortifacient potions such as birth control pills.