Half the job losses will be in Germany. It is working with its unions to agree the measures by 22 June.
The job cuts come despite the group securing a €9 billion German government rescue package, which is awaiting formal EU approval.
The group said it hoped to reduce redundancies through new working agreements, and pledged to preserve as many jobs as possible.
However, the job loss figure is more than double its previous forecast; back in April, the group estimated it had in the region of 10,000 excess jobs.
"Without a significant reduction in personnel costs, we will miss the opportunity of a better restart from the crisis," said Lufthansa labour director Michael Niggemann.
Niggemann added that without the measures, there was a risk the group would emerge from the pandemic "significantly weakened".
Lufthansa also plans to reduce its group fleet by around 100 aircraft.
