There is some silly regulations in the IRS guidlines for Domestic travel/reimbursement. My former company switched over to it.

Lets say you go to Atlanta on business. Atlanta per this IRS Publication 1542 defines Atlanta as a $38 (old publication is all I have) city. Other cities in GA are a different per-diem.

Since the projects tended to be long term, we were in one city for many months.

The IRS publication stated that if you were allowed more than this city by city amount .. .part of the per-diem would be considered income to the employee for tax purposes. So everyone had to follow this rule since the company refused to process any tax forms for the differential.

There got to be an arguement on short term vs long term staff on a project. Long term (in a corporate apartment) HAD to take this IRS ruled per-diem. Short term staff who stayed in hotels could bill 'actual expenses' that were reasonable (approved by the client). So some people gouged the client by staying 8 months in a hotel just to avoid the apartment-dictated low per-diem (and the hotels would be more $$ than monthly corporate apartments).

Out of the US .. it was totally different and varied based on the location .. pretty reasonable for most foreign cities.

Not sure if this ruling/publication currently is in force ..