Regional pay structures across ASEAN

I run reward for six ASEAN markets from Singapore: Malaysia, Thailand, Indonesia, Vietnam, the Philippines and Singapore itself, about 5,000 employees. Each country has its own grade structure inherited from acquisitions, with anything from 9 to 17 grades.

The regional president wants one structure. I agree on a common set of levels but not on common ranges, and I am struggling to explain why Vietnam and Singapore cannot share a band even with a multiplier. Range spreads, fixed allowances and thirteenth-month practice all differ. How have others set this up, and how wide are your ranges in the faster-moving markets?