The discount tariff is scheduled to take effect this weekend.

This gave shipping companies the right to introduce a discount tariff if registered at the Federal Maritime Commission.

MCI also feels that the discount tariff would allow A.T.&T. to engage in predatory pricing.

The group regularly entertained their Icelandic hosts, not in full exchange for board and lodging, to be sure, but for goodwill certainly, and sometimes for a little extra on their plates, or a modestly discounted tariff.

MCI, the nation's second-largest long-distance carrier after A.T.&T., opposes the discount tariff on legal grounds, citing the 1934 Communications Act, which prohibits a telephone carrier from unreasonable discrimination among its customers.

The discount tariff is important to A.T.&T. because it would give the company the flexibility it has sought to respond to individual customers who have been offered discounts by competing long-distance carriers like MCI and the U S Sprint Communications Corporation.