Supporters of Bradley Manning, the US Army analyst accused of leaking secrets who grew up in Pembrokeshire, want Welsh politicians to campaign for him.
He appeared at a pretrial hearing on Friday accused of passing material to Wikileaks.
Campaigners in Wales say concerns about his treatment since his arrest in May 2010 remain and political pressure from Wales is needed.
US officials have said the leaks put military and civilian lives at risk.
Pte Manning, who appeared at the hearing at Fort Meade in Maryland, was born in Oklahoma and spent almost four years at Tasker Milward Comprehensive School in Haverfordwest, and his Welsh mother Susan still lives in Pembrokeshire.
Supporter Vicky Moller, who is from Pembrokeshire, told BBC Radio Wales she had been writing to her AMs and MPs urging them to raise concerns about his treatment.
"They've made some commitment to do something about it but not enough and I'm frustrated about that but I'm sure we will get somewhere in the near future," she said.
"The Scottish National Party have spoken out already, Ann Clwyd, the Welsh MP, has spoken out and I'm confident that the assembly will do something with enough pressure."
Supporters will campaign in Cardiff city centre on Saturday, which is Pte Manning's 24th birthday.
It will be one of a number of protests taking place in Europe and America.
He is accused of passing hundreds of thousands of diplomatic cables to the whistle blowing website, detailing operational information in Iraq and Afghanistan.
His friend David House said: "As someone who has seen his decline both physically and mentally, as someone who has seen Barack Obama come out and say this man is guilty before even having a trial, I'm not sure that he can have a fair trial anywhere in the States."
The US military says the release of classified documents on the Wikileaks website about the wars in Afghanistan and Iraq may have endangered US and allied troops and civilians.
Nato chief Anders Fogh Rasmussen also condemned their release, warning that they could have had "very negative security implications".
Some of the documents published by Wikileaks contained the names of locals who had helped coalition forces.
There have also been fears such leaks could damage US intelligence sharing with other nations, as well as intelligence sharing between US agencies.