BT will slash a further 15,000 jobs this year - most of which will be in the UK - after reporting an annual loss of £134m.
The cuts represent 10% of BT's global workforce and are expected to hit contractors and agency staff.
The telecommunications giant also revealed that it has already cut 15,000 jobs in the past year - 5,000 more than previously expected.
A BT spokesman told the BBC: "Our aim is to work closely with the unions to reduce BT's total labour cost, of both direct and indirect staff, as this is critical to the success of the company going forward."
The losses have arisen following poor performance at the BT Global Services division which provides IT infrastructure to multinational companies and government departments.
Andy Kerr, deputy general secretary of the Communication Workers Union, said: "15,000 is a very challenging level of job losses, especially on the back of last year's reductions. We expect the majority of job losses to be third party - contractors and agency staff - as they were last year.
"We're working closely with the company to ensure any losses are voluntary and we're looking at new ways of finding new work and retaining permanent employees, including secondment agreements."
BT chief executive Ian Livingston said: "Three out of four of BT's lines of business have performed well in spite of fierce competition and the global economic downturn. However this achievement has been overshadowed by the unacceptable performance of BT Global Services."
In March BT introduced a pay freeze for all UK-based staff.
BT said it would also have to make £525m-worth of pension contributions in each of the next three years to address the scheme's deficit.
Earlier in the week unions warned BT executives not to take bonuses in the wake of thousands of job cuts.