"If you're not very careful, (selling arms abroad) can very quickly become a deal with death," Gabriel, who is also vice chancellor, warned recently on public television.
Normally, the position of deputy chancellor is largely a symbolic one.
But Gabriel, a Social Democrat, is taking advantage of the absence on holiday of conservative Chancellor Angela Merkel to lobby publicly for a topic close to his heart.
Exporting arms was already an issue for his Social Democratic Party (SPD) during last year's general election campaign, but with the crisis in Ukraine, it has taken on added currency.
Gabriel believes that European sanctions against Moscow do not go far enough, and last week he blocked a major contract for German company Rheinmetall to provide a fully-equipped training camp to Russia.
The minister is not looking to change Germany's current laws on arms exports.
But he wants the authorities to be much more watchful when awarding export licences, particularly with regard to the country buying the weapons and their record on human rights.
In 2013, Merkel's previous administration authorized €5.8 billion worth of arms exports, 62 percent of which were destined for non-NATO countries such as Algeria, Qatar and Saudi Arabia, with Gabriel particularly concerned about the latter.
But the minister's plan, seen by some as an attempt to reach out to the opposition Greens and far-left Linke party in the distant eventuality of a post-Merkel alliance, is rattling some conservatives.
The head of the Christian Social Union (CSU) party, Horst Seehofer, accused Gabriel of acting "without a concept and without a compass" and of endangering jobs.
"German companies will disappear from the market or relocate abroad," he warned.
The CSU is the Bavarian sister party of Merkel's Christian Democratic Union and the wealthy southern state is home to companies such as Airbus Defence and Space, tank maker Krauss Maffei Wegmann – which plans to tie-up with French rival Nexter – and guided missile maker Diehl.
Germany's defence industry is tight-lipped about its actual sales, preferring instead to publish its output.
In 2011, the most recent data available, the sector's output amounted to €22.6 billion.
It employs nearly 100,000 people directly while more than 200,000 are employed by sub-contractors and suppliers.
According to the Stockholm International Peace Research Institute (SIPRI), Germany is the world's third-biggest exporter of arms, after the United States and Russia.
Germany's own security and defence industry federation, BDSV, is more modest.
"We're definitely among the top 10," a spokesman said.
But according to the business daily Handelsblatt, weapons is one area where Germans are not proud of their export prowess.
But in addition to exports of tanks or missiles, pacifists are angry about exports of small arms, such as the guns and pistols made by Heckler & Koch, which has annual sales of more than €200 million.
In a fervent plea to ban arms exports, former chancellor Helmut Schmidt described smaller hand-held weapons such as machine guns and hand grenades as "today's weapons of mass destruction".
Generally speaking, "I think it's perverse to send weapons instead of soldiers," he said.
Gabriel's SPD party colleague, Foreign Minister Frank-Walter Steinmeier, has for months been calling for Germany to become more directly involved in the resolution of international conflict hotspots.
As for the industry itself, "we would like the government to tell us what its position is," BDSV chief Georg Wilhelm Adamowitsch said recently.
Last week, defence technology group Rheinmetall issued a profit warning in the wake of Gabriel's decision to block its Russian contract, sending its shares sharply lower on the stock market.
Gabriel is to meet labour representatives of some of the market players in mid-August.