Deductions Allocated to Effectively Connected Income Under Regulations Section 1.861-8. This form is used by any foreign corporation that is required to file Form 1120-F and is - or is treated as - engaged in a trade or business within the United States at any time during the tax year. This form must be attached to its Form 1120-F. The form reports the amount of the foreign corporation's deductible expenses that are allocated and apportioned under Regulations 1.861-8 and 1.861-17.