Myanmar nationals Wa Lone, 31, and Kyaw Soe Oo, 27, were arrested a month ago after receiving documents from two policemen during a dinner in Yangon.
They were detained under the colonial-era Official Secrets Act after they left the restaurant for alleged possession of classified documents obtained "by deception".
The pair had been reporting on the military campaign in Rakhine state that has forced some 655,000 Rohingya Muslims to flee over the border to Bangladesh since August, violence the UN has condemned as ethnic cleansing.
Reuters insists their reporters have done nothing wrong, while their families have suggested the pair were set up.
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The US and EU have led global calls for the journalists to be freed, while Amnesty International late Tuesday repeated its appeal for their immediate release.
"They have done absolutely nothing but carrying out their legitimate work as journalists," said James Gomez, Amnesty International's Director for Southeast Asia and the Pacific.
Former US president Bill Clinton also weighed in on the issue.
"A free press is critical to a free society-the detention of journalists anywhere is unacceptable," he tweeted on Monday.
The case has cast a spotlight on Myanmar's troubled transition to democracy after nearly five decades of military rule.
It touches on both slumping press freedom and the Rohingya crisis, two issues that have raised questions over the country's ability to shake off the legacy of junta rule.
Much of the Buddhist-majority population supports the army in what it calls a legitimate campaign against Rohingya militants after attacks against border guard police killed about a dozen.
The military has severely restricted access to northern Rakhine state to journalists, aid groups and observers.
They must either be charged at Wednesday's hearing or released.
Reuters has vociferously denied any wrongdoing on behalf of their reporters, defending their right to report on an issue of global significance.
A slew of legal cases against journalists have compounded disappointment among those hoping the civilian government of Aung San Suu Kyi would usher in a new era of freedom.
Her administration shares power with an army that still controls all security policy and other key levers of government.