Power, or more precisely perceptions of power, are critically important in understanding the commercial negotiation process. From a commercial negotiation point of view (under any circumstances, either integrative or distributive approach), CIPS is interested in power from both a personal and organisational perspective.
When you are negotiating on behalf of your employer, you bring the power of your organisation (its brand, reputation and purchasing spend) as well your own personal power (6 sources of personal power, based on French and Raven's power base model) to the negotiation.
In both integrative and distributive approaches, personal power plays an important role. It helps both parties push through negotiating barriers and secure commitment and final agreement LO 1, AC 1.3

In order to break vicious cycle of blame, procurement will need to use their negotiation and conflict management skills,adopting a collaborative and integrative approach. Your first action should be to establish the facts that led to the situation where the relationship broke down. Most day-to-day relationship between buying organisations and suppliers do not of course involve procurement staff, so you will need to consult with your business partners internally to establish their point of view of where the issue and sources of conflict are. You should also contact the supplier and get their side of the story - this is particularly to when you have previously identified the supplier as critical or otherwise important to your operations. Ideally you will be able to apply principled negotiation here, separating the people from the issue, focusing on interests and not positions,and then looking for options of mutual benefits.