There are thought to be hundreds of tunnels along the border
Palestinian supporters in Egypt are taking the government to court to prevent them building an impregnable barrier along the border with Gaza.
The group, which includes support from UK and US citizens, say the plan is a violation of international law and breaks agreements with the Arab League.
But the Egyptian government say the barrier is needed to protect its sovereignty and security.
The court is expected to rule on the case in June.
But even if the decision goes in the group's favour, the government has ignored such rulings in the past, says Christian Fraser, the BBC's correspondent in Cairo.
The plaintiffs are supported by Mohamed ElBaradei, the former head of the UN nuclear watchdog, who is now the leader of the National Coalition for Change.
He says as well as stopping weapons, the barrier will prevent much-needed food and medical supplies entering the Gaza Strip.
When it is finished the wall will be 10-11km (6-7 miles) long and will extend 18 metres below the surface.
It is to be made of bomb-proof steel.
The blockade of Gaza by Egypt and Israel was tightened after the Hamas movement took control of the territory in 2007.
The tunnels are a conduit for commercial goods, including food and medicine, but are also widely believed to be used for smuggling cash and weapons to Hamas.
Israel and Egypt say they deny entry to all but basic humanitarian supplies, in order to prevent Gaza's Hamas rulers firing rockets at Israel.