My parish priest teaches RCIA yet refuses to address the issue of contraception. Can I withhold money from my parish tithe for his refusal to teach on such an important topic?
You are well within your rights to withhold money from a priest who is refusing to address a pressing moral problem—indeed, a moral crisis—that is affecting his congregation. One of the precepts of the Church (CCC 2043; CIC 222) is that we are obligated to use our money to support the Church, but this does not mean that we have to support a particular part of the Church that we believe is not doing its job.
Because of the seriousness of this issue, you might consider taking the money you would otherwise have given for teaching in your parish and donating it to a Catholic organization that takes a strong stand against abortion and contraception. You might even inform your pastor that you are doing this.
The Code also states that the Christian faithful "have the right and even at times the duty to manifest to the sacred pastors their opinion on matters that pertain to the good of the Church" (CIC 212).