LONDON (AP) — British companies have until midnight to publish their gender pay gap, as Prime Minister Theresa May promised to tackle the "injustice" of unequal earnings between the sexes.

The government has told all firms with more than 250 employees to publish by Wednesday the difference in median hourly wages earned by men and women. More than 8,800 of about 9,000 companies have already done so.

Seventy-eight percent showed a pay gap in favor of men, while 14 percent favored women and 8 percent had no gap.

The government says Britain's overall pay gap is 18.1 percent.

In an article for the Daily Telegraph, May said the pay gap was one of "the burning injustices which mar our society."

Firms are supposed to produce a plan to narrow the gap.