More than 300 employees of a coal mine in southern Hungary returned to work Thursday after a 20-hour strike that posed the first worker challenge to the strict economic policies of premier Karoly Grosz.

In negotiations with senior government officials, the strikers won a promise the government would try to iron out a quirk in a new income tax law that allows workers on sick leave to earn more than those working regularly.The strikers at the Komlo mine 100 miles south of Budapest threatened to halt work again if parliament does not remove this quirk.

In addition, the government instructed companies to pay bonuses to miners who complained they had lost 30 percent to 50 percent of their bonuses under the new tax laws.

The daily Magyar Nemzet published the text of a letter sent by the strikers to Grosz, who in May became Communist party leader, urging him to settle "the oft-repeated problems" of miners at Komlo, 100 miles south of Budapest.

The letter attacked the personal income tax introduced Jan. 1 as part of Grosz's attempts to stimulate the stagnating economy. It said the tax "does not stimulate production or the undertaking of extra shifts."