Two ships from Sweden and Estonia on Thursday left port to begin preliminary surveys for a new examination of the wreck.
The ship, which was sailing from Tallinn to Stockholm, went down in the early hours of September 28th, 1994.
There were only 137 survivors and 852 people perished in one of the worst maritime disasters of the 20th century.
After deciding not to salvage the wreck, Sweden, Estonia and Finland agreed in 1995 to designate it a final resting place and make it illegal to disturb the site.
But the laws banning dives were recently amended in order to allow a re-examination of the wreck after a documentary cast doubt on the findings of an official investigation into the sinking.
The new probe is being conducted by accident investigation authorities in Sweden and Estonia.
Jonas Backstrand, chair of accident investigations at the Swedish Accident Investigation Authority (SHK), told AFP the two ships involved in the study would leave port on Thursday and converge near the site, which is in international waters, around midnight.
“The actual diving begins tomorrow,” he said.
After a preliminary examination, a larger survey would be conducted at a later date, which SHK estimates will be completed in the spring of 2022.
The original inquiry concluded that the disaster was caused by the bow door of the ship being wrenched open in heavy seas, allowing water to gush into the car deck, and the countries involved have been reluctant to re-examine the issue.
Survivors and relatives of those killed have fought for over two decades for a fuller investigation.