According to OKP's statement to the SGX, its subsidiary and the three executives face charges under the Building Control Act - which is under the purview of the Building and Construction Authority - and/or the Workplace Safety and Health Act, under the Ministry of Manpower.
A BCA spokesman said: "Prosecution action is being taken under the Building Control Act, following investigations into the viaduct structure under construction at the Pan-Island Expressway."
The authority did not comment on the findings of the investigations, which have taken nearly a year.
The MOM said a Stop Work Order on the site issued immediately after the incident is still in force.
The fate of the viaduct, which would offer motorists a more direct connection to the westbound PIE and Upper Changi Road East by 2020, is now uncertain.
The Straits Times understands the Land Transport Authority, which awarded the project to Or Kim Peow Contractors for $94.6 million in 2015, has three options - namely, to appoint another contractor to finish the job; re-design the structure with reinforcement before continuing the works; or tear down what has been built and redo the whole project.
A senior engineer said the course of action will depend on what the investigations have unearthed.
"If it is a technical fault for one particular location, you may be able to continue by say, replacing a beam or column.
But if there's an underlying problem that extends to all structures, then you may have to redo the whole thing."
He added that the fact that the investigations have taken so long - and the fact that charges are filed before findings are made known - indicate a likelihood of the latter.
If so, the project will not see light of day till much later than 2020. On the morning of July 14, a 40m section of the viaduct collapsed, with preliminary findings pointing to corbels - support structures - giving way.
Experts had pointed to a design flaw as one possible cause for the corbel failure. Post-incident checks also revealed cracks at 11 other locations along the viaduct, an indication of a problem that is not isolated. It also emerged that a consultant from CPG - OKP's sub-contractor - who designed the viaduct was also the supervisor who checked the construction works.