Frenchmen Antoine Deltour and Raphael Halet, both former employees of auditing firm PricewaterhouseCoopers (PwC), are accused of leaking thousands of documents to journalist Edouard Perrin.
The documents revealed showed how Luxembourg granted huge tax breaks that saved firms including Apple, IKEA and Pepsi billions of dollars in taxes, at a time when Jean-Claude Juncker - now head of the European Commission - was Prime Minister.
The maximum penalty available was a jail sentence of 10 years for the charges against the two whistleblowers, which include stealing documents, revealing business secrets and violation of professional secrets.
"Deltour and Halet are not really whistleblowers, and Perrin has broken the law," deputy state prosecutor David Lentz told the court on Tuesday as he summed up the prosecution's case two weeks after the trial began.
He added, "We are here to deliver justice. They must be judged on what they did, this trial has to take place. It's disagreeable, but my job is to protect society against all abuse of the law."
A verdict is not expected until mid-June but the demand for a custodial sentence have been roundly condemned, including by Brussels-based campaign group Corporate Europe Observatory.
Its researcher and campaigner Martin Pigeon told this website, "It is scandalous that none of the tax dodgers exposed in the Luxleaks scandal is facing anything while the two persons we owe it to are facing heavy fines and jail time.
"It is also worth mentioning that the prosecutor justified requesting such penalties by referring to 'the EU trade secrets directive widely approved in the European Parliament two weeks ago'".
Pigeon added, "Contrary to the denials of the text's supporters, this is a very strong indication that the trade secrets protection argument can be used to prosecute journalists and whistleblowers."
The directive has already been backed by Parliament but CEO, he said, is urging member states not to approve the text.
Sven Giegold, a German Greens/EFA group MEP, was also particularly scathing of the prosecutors, describing the call for a prison term as outrageous.
The deputy, who repeated his call for the Commission to table a directive for the protection of whistleblowers, said, "Let us remind ourselves that these actions were taken to uncover illegal activity and no one will understand why they should be sent to prison. This is at odds with all sense of justice and underlines the need for better legislative protection for people like Deltour and Halet."
Further criticism of the prosecution's call for prison sentences came from Carl Dolan, of Transparency International, who told this website, "Deltour and Halet should be protected and commended, not sent to prison. The information they disclosed was in the public interest. The fact that the European
Commission has made sure that the details of the tax deals will now be shared with all other EU governments demonstrates this all too clearly."
The two former PwC employees have both defended their actions.
Deltour, who was the first person to leak documents to Perrin, told the court last week he was proud to have opened up the issue of tax breaks for multinationals.
Halet said he had decided to do his duty as a citizen after he was shocked by the size of the tax breaks.
In the past two years, the EU has pushed through tougher rules on taxation in the wake of the LuxLeaks release.
It was the biggest expose of its kind until the recent publication of the Panama Papers, which revealed links between a number of international leaders and offshore shell companies that can be used to hide or launder wealth.
In a video message to a public hearing in Parliament last week, the French-born Deltour said that as whistleblowers often exposed things of a supranational interest, it was necessary to have EU-wide standardised laws to protect them.
He said he believes whistleblowers should remain anonymous, be offered legal support and advice and entitled to compensation for economic losses they incur.
He also called for the creation of an independent body to rule on the legal immunity in whistle blowing cases.
Laws should also be enacted, said Deltour, which give whistleblowers the possible right to compensation.
The conclusion of the trial comes after MEPs recently backed the new trade secrets directive which campaigners say will make life harder for whistleblowers.
According to a survey by Transparency International only four member states currently have domestic legislation on the protection of whistleblowing.