"Any move of production and research and development has to be approved by us," union negotiator Stefan Leiding told the newspaper.
The head of the metal workers' union IF Metall, Anders Ferbe, welcomed the news.
"Production won't be moved from Södertälje, Oskarshamn, or Luleå without the union being in agreement," he said in a statement.
The deal would come into effect if Scania accepts Volkswagen's bid for the company. Volkswagen already owns 63 percent of share capital in the Swedish truck maker and offered 200 kronor ($31) per share for the remaining stock.
Union negotiator Leiding underscored that he did not have an opinion about whether or not the owners should accept or reject the Volkswagen bid.
The proposed takeover by Volkswagen has generated considerable interest since it was first mooted in February. After the initial offer, two of Scania's owners, Skandia and AP4, said they were unwilling to sell their stock. Scania's board has been dissecting the offer ever since.
In a statement issued in March, the Scania board's independent committee made its objections clear.
"Our assessment is that the current offer does not reflect the long-term value of the company and a fair share of the synergies," said committee chairwoman Åsa Thunman.