Central excise on job works

Hi,

There is three companies involved. Comp A, B & C. Comp A sources job works from Comp B and transfer it to company C for execution. Company A does not execute any work itself. Company B releases material to Company A with a challan. At the time of payment Company B pays to Comp A , and Comp A after deducting its agreed share passes the balance to Comp C. What should be the challan and excise rules applicable to Comp A. Its really very urgent.