Yes, a creditor can object to your bankruptcy filing if they have grounds to do so. For instance, fraud or knowledge of hidden assets. Depending on the reason for the objection, the creditor may seek to have only their debt survive your bankruptcy. The US Trustee can also object to your bankruptcy filing (if you are over income on the means test for a Chp 7 is a good example).
The above answer is fine, but I want to add - a creditor may also object to your exemptions, if they are improperly utilized.
That said, by far the most utilized objection by creditors in a Chapter 7 case is that under §523 for fraud of the creditor, as stated more eloquently above.