All residents in the EU member state will get a pass entitling them to ten free journeys of any length on the country's railways.
The free ticket, agreed by government ministers at the weekend, is part of a raft of measures like higher welfare payments and a VAT cut, meant to stimulate economic activity.
The 10 journeys will be valid between 1 July and 31 December 2020, with the aim of encouraging people to go away for the weekend and spend money in the ailing tourist sector.
The move has caused some controversy, however, because the country's public railway company SNCB says it was not consulted on the decision.
SNCB boss Sophie Dutordoir took to social media on Sunday to complain about the government's approach and warn about the possibility of overcrowding.
“The way in which a decision was taken yesterday without any consultation raises serious questions,” Ms Dutordoir said in a message posted on Twitter.
“The SNCB is therefore requesting immediate consultation and all necessary assistance to avoid any risk of overcrowding of trains and platforms.”
If all those eligible for the rail pass use their tickets the policy will create around 96 million extra rail journeys.
Koen Geens, the country's the federal justice minister, said: “The intention was to get domestic tourism back on track because the trains are severely underutilised. I hope that all goes well, and that we can help guarantee safety.”
He also apologised for the lack of consultation with SNCB and said Ms Dutordior should have been contacted.
Belgium lifted most of its remaining lockdown measures on Monday, reopening bars and restaurants with some social distancing measures in place.
The country went into a full lockdown on 18 March. Measures seem to have been relatively successful in defeating the virus, with the country recording no excess mortality since 11 May.
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