Amnesty International and Oxfam supporters hope to pressure her to close loopholes in legislation being drawn up to prevent Britons selling guns to conflict zones.
Oxfam claims British arms dealers have shipped or brokered more than 1,200 tons of military equipment to war zones since Labour came to power.
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The carnage wrought by gun-runners is chilling
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Justin Forsyth, Oxfam
The cardboard cut-outs of AK47 guns carried signed messages from actress Helen Mirren, former Take That and Big Brother star Mark Owen, the Bishop of Oxford, the Right Reverend Richard Harries, and members of the public.
They were dumped outside the minister's constituency office in Leicester.
Oxfam policy director Justin Forsyth said: "Labour came to power promising to crack down on gun-runners wherever they are based.
"Although they have been a vast improvement on previous governments, this new law leaves the backdoor wide open for Britain's gun-runners to continue brokering and transporting guns to some of the world's bloodiest conflicts.
Transparent system
"The carnage wrought by gun-runners is chilling."
The government is set to consult on the legislation in January.
A DTI spokesman said the UK already had one of the most transparent systems in the world for export controls and the Export Control Act would significantly tighten controls on arms trafficking and brokering.
"Extra-territorial controls will apply to UK persons wherever they are located when they seek to trade in torture equipment and long-range missiles, or arms to embargoed destinations," he said.
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