News agency Reuters reported that most of the parliamentary leadership of Chancellor Merkel's Christian Democratic Union (CDU) raised objections to the sale at a meeting on Monday. The environmentalist Greens planned to raise the issue in the Bundestag on Tuesday.
News magazine Der Spiegel reported at the weekend that the German government had given the green light to the sale of Leopard 2 battle tanks, which would reap more than €1 billion for the country's arms industry but reverse its long-held policy not to supply heavy weaponry to the Arab kingdom.
Reuters reported that key members of the party's parliamentary group raised vocal concerns, including the chairman of the foreign affairs committee, Ruprecht Polenz, Bundestag president Norbert Lammert and the party's human rights expert Erika Steinbach.
They argued that breaches of human rights by Saudi Arabia raised questions about the sale. Lammert pointed out Saudi Arabia had recently deployed tanks to help suppress the anti-government protests in neighbouring Bahrain.
Concerns about Israel's safety have also been expressed.
The Greens' parliamentary leader, Jürgen Trittin, said the supply of tanks to the autocratic regime would breach the tradition of Germany's Middle East policy.
“Such equipment is not usually supplied to such areas,” Trittin told public broadcaster ARD on Tuesday morning.
Saudi Arabia had only recently been involved in “steamrolling” the pro-democracy movement in the gulf state of Bahrain, he added.
On top of additional arms supplies to Algeria valued at about €10 billion, the government was entering dangerous new territory.
“It shows that there is no red line any longer for the federal government in Middle East policy,” Trittin said.
Der Spiegel reported that the deal had been approved by the government's Security Council, a cabinet group made up of the chancellor and key ministers and which examines all major arms deals. The government has so far declined to comment.
Reuters also reported that Saudia Arabia has already purchased 44 battle tanks from Germany.
Merkel's junior coalition partners, the pro-business Free Democratic Party (FDP) has also raised concerns. The party's defence expert, Elke Hoff, told broadcaster ARD: "They may do it. The question is whether it is accompanied by the necessary political sensitivity and how it is received by the public."