The Interstate Commerce Commission announced late yesterday that bus companies will be permitted to increase fares by 6 per cent across the board after one day's notice.

Bus companies had sought permission for the "emergency" increase as part of a two-step, 13 per cent package that is opposed by the Justice Department.

Technically, the ICC suspended the permanent 6 per cent fare increase but said it would permit the boost to take effect on a temporary basis through May 30 while the agency investigates the bus companies' justification for their request.

P.J. Campbell, chairman of the Chicago-based National Bus Traffic Association, an industry organization that sets interstate rates, last night said he had not seen a copy of the ICC order and could not say when bus fares would be increased.

Because of apparently necessary paper work associated with the short-term rate filing, the 6 per cent increase probably will not take effect until early next week, Campbell added.

Thereafter, the bus lines must submit to the ICC complete details on the overall 13 per cent package by May 1. The agency then will determine if the 6 per cent boost becomes permanent and if the proposed 7 per cent additional rise, scheduled for May 15, will be permitted.

The Justice Department told the ICC that bus companies had not provided evidence to support an emergency fare increase following rate boosts totaling 35 per cent in the last three years.