The German government has said the company's plans to export three liquefied natural gas plants to Iran were approved earlier this year because the plants did not fall under any category of goods banned from export.
However, Merkel spokesman Thomas Steg said the chancellor had repeatedly made clear that moral considerations, and not just export bans, should play a role in such deals.
Firms should show some restraint in their dealings with Iran, though this could not be prescribed, he said.
"The government is expecting some sensitivity from businesses," Steg told a regular news conference.
Germany is one of six nations leading efforts to rein in Iran's nuclear program.
The West accuses Iran of planning to build nuclear warheads under cover of a civilian power program. Iran, the world's fourth largest oil producer, denies the charge.
Israel's Foreign Ministry said last week it was disappointed by Germany's decision to allow the gas plants deal, saying it contravened the spirit of world powers' sanctions against Iran over its nuclear program.
A German source has said the deal concerned engineering firm Steiner Prematechnik Gastec GmbH.
(Reporting by Hans-Edzard Busemann; Writing by Kerstin Gehmlich, editing by Madeline Chambers and Mary Gabriel)
