。
The soldiers refused to obey that order.
Literal
Soldiers [topic-は] that order [target-に] obey [nominalizer-こと] [object-を] refused.
拒否した (refused) is the natural verb here — it means to refuse or reject an action or request, in contrast to 否定 which means to deny or negate a claim. The nominalization ~ことを (turning 'obeying that order' into a noun phrase) lets the action serve as the direct object of 拒否する.