Hired, then given paycut?

I accepted an offer for a really great job. Have been here 8 months. They asked me to start taking on some new responsibilities that led to a possible promotion... Well after doing the new job for 4 months the just told me a few weeks ago the new position pays less..I would essentially go from 47k to 41k... Told them I am not comfortable with this... They seem to really be trying to force my into this position now and rate of pay, and im afraid I don't have a choice to stay at my current pay and old position. So upsetting, we just found out we are pregnant and what not...Any advice on how to handle this? Anyone else been in this situation?