The band's last album, A Beautiful Lie, was released in 2005
Actor and musician Jared Leto has criticised his former record label after it claimed his band failed to fulfil its contract.
EMI is suing 30 Seconds To Mars for $30m (£16m) in Los Angeles, saying it failed to produce the three albums stated in their contract.
But Leto insists the contract was legally "null and void".
EMI said it hoped to "resolve these matters amicably" so it could carry on "working in partnership" with them.
A spokeswoman for the record label said: "EMI's relationship with 30 Seconds to Marshas been extremely rewarding and successful for both the band and the company.
"The hard work of EMI's global team and of the band has resulted in sales of three million albums and singles, multiple awards and a growing, global fan base."
However, Leto told fans on his Myspace website that the group had never been paid for the work they produced.
"If you think the fact that we have sold in excess of 2 million records and have never been paid a penny is pretty unbelievable, well, so do we," he said.
According to the lawsuit, which was filed on Friday, the band "repudiated" a 1999 contract in July.
Their last album, A Beautiful Lie, was released in 2005.
Leto said despite rumours, the band were "not calling it quits" and are "incredibly happy, healthy and very much together here" recording their new record.
We would always do our best to avoid a fight, but sometimes it's important to stand up for what you believe in
He said that the band had originally signed a nine-year contract, but under Californian law a contract cannot run for any longer than seven years.
"Roughly 45 days ago we exercised our legal right to terminate our old, out of date contract, which, according to the law is null and void," he said.
He added that many of the people they had worked with at the company had been fired and it was no longer the place it once was.
"We did not want to take this public, but we felt it best to explain our point of view to you," he said.
"We will always remain grateful to the people at Virgin/EMI who were so integral to our success.
"And we hope that, above all, we can find a resolution to this in as civil and kind a way as possible."