In the book "Field Guide to Project Management" by David I Cleland, there is a discusson on page 282 about "Conflict in Negotiations". As the book mentions, PMI (the Project Management Institute) outlines eight project management functions that can be a source of conflict.
To paraphrase from the book, the areas are:
Scope: what is to be done (results, products, services)
Quality: what measures, what steps to be taken
Cost: financial outcomes, savings, ROI
Time: deadlines, resources, when complete
Risk: what risks are accepted, avoided, deflected
Human Resources: what resources, what skills, availability, competency
Contract/Procurement: cost, requirements/specifications, when, how, what, where
Communciations: when, how, to whom, contains what
There are several ways to approach handling conflict (see the Guide to the PMBOK), however the important point to keep in mind is we must confront the issue(s)and work with the individuals or groups to come to a win/win outcome.
Unresolved conflict can often lead to bitterness and resentment, which can linger and rise up later to sabatoge your project.