A Skanska-DPR joint venture is leaving its role as general contractor of Apple's "spaceship"—the ring-shaped main building of the tech giant's new corporate headquarters now under construction in Cupertino, Calif.

Skanska "will transition completely off the project in the next several weeks," said an internal email sent to Skanska employees and obtained by the Silicon Valley Business Journal.

Rudolph and Sletten, a division of Tutor Perini, is expected to complete the core and shell of the main building, compared in scope and scale to the Pentagon. It had been assumed that Skanska-DPR would perform the work.

Gerald Pfeiffer, business manager for the International Brotherhood of Electrical Workers Local 332, San Jose, Calif., said there have been more than 100 electrical tradesmen alone at the site. He said there was no evidence of major cost over-runs or work stoppages because of the change in general contractors.

Eddie Estrada with International Union of Operating Engineers Local 3, Morgan Hill, Calif., said it was business as usual at the job site. "We haven't heard anything from that site since the change."

Additional information concerning the rift between the Skanska JV and Apple has not been revealed, but the firm, whose market capitalization passed the $700- billion mark this year, has a reputation for being difficult to work with. Several contractors have been fighting to recover losses from a bankrupt former Apple partner for the construction of a sapphire-glass manufacturing plant in Mesa, Ariz.

Though Apple negotiated all construction deals, it reduced its risk by placing contracts in the name of its partner, GT Advanced Technologies, the company said in Delaware bankruptcy court in 2014. Apple, which still owns the facility in Mesa, says the site is being transitioned into a $2-billion data center.

The email to Skanska employees said that the contractors "and our confidential client were unable to come to an agreement during negotiations for the revised scope of work for its research and development campus in California."

Local reports have identified Apple as Skanska's client through city permits. Several calls to Edith Sandoval, Apple's project manager for the Cupertino job, were not returned.