1
general::
Also, on behalf of. 1. For someone else, as someone's agent or representative. For example, In behalf of the board, I want to thank you for your help, or Joan was speaking on behalf of the entire staff. [c. 1300] 2. For someone's benefit or interest, as in He was collecting the dues in my behalf. [Late 1500s] Some authorities insist that in behalf of be used only to mean "for someone's benefit" and on behalf of only to mean "as someone's agent." In practice, however, the terms are so often used interchangeably that this distinction no longer has a basis.
American Heritage Idioms
2
general::
Phrase(s): in behalf of someone [and] in someone’s behalf; on behalf of someone; on someone’s behalf; in someone’s name
[doing something] as someone’s agent; [doing something] in place of someone; for the benefit of someone. • I’m writing in behalf of Mr. Smith, who has applied for a job with your company. • I’m calling on behalf of my client, who wishes to complain about your actions. • I’m calling in her behalf. • I’m acting on your behalf.
McGrawhill's American Idioms And Phrasal Verbs