FILE PHOTO: Linde Group headquarters is pictured in Munich, Germany August 15, 2016. REUTERS/Michaela Rehle/File Photo

MUNICH, Germany (Reuters) - Finalizing a merger with Praxair PX.N is likely to take "several months", the chief executive of Linde LING.DE said in a letter to a shareholder association, reiterating he saw no need to ask shareholders to vote on the $65 billion deal.

German industrial gases group Linde and U.S. rival Praxair announced in December their intention to merge to create a global leader, saying at the time they expected to execute a definitive business combination agreement “as soon as possible” in the coming months.

In a letter to German retail-shareholder association DSW filed with the U.S. Securities and Exchange Commission, Linde CEO Aldo Belloni rejected criticism he was not informing shareholders sufficiently about the progress of discussions with Praxair.

He also defended his decision not to call a shareholder meeting to approve the deal.

“I am sure you will understand that developing, negotiating and documenting the details of such a complex merger naturally takes time,” he wrote in the letter dated March 7.

“Speaking from experience with other (often less complicated) mergers, we foresee the whole process taking several months.”

Linde is expected to give an update on its negotiations with Praxair at its full-year results on Thursday.

A source close to the deal said this week the detailed so-called business combination agreement would not be signed this month, due to delays caused by German unions, who fear their influence in a combined company will be diminished.