Britain's biggest coal producer, UK Coal, has seen its half-year losses spiral amid production problems and the cost of a long-running dispute.
Kellingley Colliery was hit by a series of 24-hour strikes
Pre-tax losses at the Doncaster-based company grew to £5.8m in the six months to 30 June from £0.8m a year ago.
In June, pit workers at its Kellingley Colliery in West Yorkshire ended four months of industrial action over new working arrangements.
And production at its deep mines had been disappointing, the company added.
Chief executive Gordon McPhie said: "The second half performance should improve with fewer production gaps at the deep mines and a return to full production at Kellingley Colliery."
Workers had staged a series of 24-hour strikes in protest at plans by UK Coal for longer shifts to boost output and absorb 180 jobs from the doomed Selby coalfield.
Half-year sales at the company, formerly known as RJB Mining, plunged 24% to £228m.