Compensation wage issue

I work for an Indian MNC, where recently, without any written intimation from HR, all associates were asked to bill 9 hours to clients, by our leadership/managers. For this increase in associates efforts from 8.5 hours to 9 hours (7% increase), company hasn't compensated associates. When I joined this company, during HR round, it was mentioned by HR manager and Head of my department that the billable hours would be 8.0 hours but considering two tea breaks (15 min each) + lunch breaks (1 hour), associates have to be in office for 9.5 hours. Later billable hours were increased from 8 hours to 8.5 hours and now this has again increased to 9 hours. Associate's efforts are increasing but the salary component is not increasing for direct revenue gains by the company. Company HR has suggested that this decision is in-line with company policy which was signed by associates in joining letter but I can't see any points related to this in my joining letter. It has one vague point stating that "employees have to follow certain changes in the policy". How is "certain policy" interpreted as anything related to employee wage? Can company be sued for this?