Work Permit And Visa

work collegue and friend of mine is in an unusual situation - he has a work permit and non B issued to him stating that he is working for an employer in bkk - but is infact working as a teacher at a school in bkk -unrelated business - the stated place of work shown in his visa and work application is no way related to what he is actually doing -- his big problem is that the salary he is shown to be getting is not what he is really receiving each month the work permit shows 50 K per month and he receives 35K and with tax being paid on the 50K to comply wth the the visa requirments - this situation has existed for the past two years == the reality is that the employers - the one he is shown to work for is a large business in bkk - what is his legal standing in regards to if he were to claim the difference of 15K per month as both his actual and so called employer are of course closely linked to each other -- but unrelated types of business - but obviously in breech of regulations as the documents lodged with immigraton and labour office are in fact false statesment of the fact. he is concerned that he will be in trouble if this comes to light - but what about the employers ???????