"A suit brought by the members of parliament Christian Ströbele, Claudia Roth and Katja Keul was filed on Friday" with the Constitutional Court, the spokeswoman added.
The Greens, who oppose the reported deal, have asked the Court to rule on whether the government is entitled to grant an export licence for the tanks without informing parliament.
Press reports recently suggested that Saudi Arabia would be buying 200 Leopard-2s, Germany's main battle tank which is also produced under licence in Spain, for a multi-billion-euro sum.
Chancellor Angela Merkel and her government have refused to comment on the reports, saying such matters are confidential and decided by the federal security council, a panel which rules on arms exports and which is chaired by the chancellor.
"Deliberation and decisions by the federal security council are secret for good reason," Merkel has told the press.
For decades Germany has declined to sell such heavy weapons to Saudi Arabia because of concerns over human rights and fears for Israel's security.
Opposition politicians and even some members of Merkel's ruling centre-right coalition have slammed the reported tank sale, particularly in light of pro- democracy uprisings throughout the Middle East.