DUESSELDORF, Germany (Reuters) -Germany's IG Metall union on Tuesday said it had preliminary talks with Carlyle on the investment firm taking a majority stake in Thyssenkrupp Marine Systems and agreed to push for an agreement as quickly as possible.

In a newsletter seen by Reuters, the union however insisted that a stake sale to private equity investors could only happen if the state stepped in as well to secure the conglomerate's naval shipbuilding activities.

The economy ministry was not immediately available for comment.

"A first round of negotiations in a small group is scheduled for the beginning of May," IG Metall said, adding that Carlyle was carrying out due diligence about taking a majority stake.

Thyssenkrupp said last month it was considering selling a stake in its Marine Systems unit. Carlyle had confirmed its involvement in the talks but declined to elaborate.

Thyssenkrupp is aiming to sell a stake of around 25% in the unit mainly due to the burden of providing billions of euros of guarantees to clients.

"...a sale to private equity investors can only happen if the state assumes its responsibility and steps in to secure naval shipbuilding as a key technology in the long term," the union said.

"There is currently broad political support for this."