The Secretary may only decline to approve a proposal for one of five specific reasons:

(a) The service to be rendered to the Indian beneficiaries of the particular program or function to be contracted will not be satisfactory;

(b) Adequate protection of trust resources is not assured;

(c) The proposed project or function to be contracted for cannot be properly completed or maintained by the proposed contract;

(d) The amount of funds proposed under the contract is in excess of the applicable funding level for the contract, as determined under section 106(a) of the Act; or

(e) The program, function, service, or activity (or a portion thereof) that is the subject of the proposal is beyond the scope of programs, functions, services, or activities covered under section 102(a)(1) of the Act because the proposal includes activities that cannot lawfully be carried out by the contractor.