Associate professor Jacque Alderson and her team at the University of West Australia performed independent analysis of both bowlers in Perth on Nov. 29.
The players have 14 days to lodge written appeals to the ICC against the UWA's findings.
In Samuels' case, if he is reported again for a suspected illegal bowling action within the next two years, he will undergo a similar independent biomechanical analysis.
According to the ICC, If Samuels bowling action is found illegal, "whether it is for his quicker deliveries or any other type of delivery, he will be automatically suspended from bowling in international cricket for a minimum period of 12 months."
Shillingford and Samuels have a history of being reported and suspended from bowling in international cricket.
Shillingford was reported in November 2010 and resumed bowling in June 2011, while Samuels was reported in February 2008 and resumed bowling in September 2011 after the pair underwent remedial work on their bowling actions and further testing.
Shilligford has taken 65 wickets in 14 test matches since making his debut against South Africa in 2010. Samuels, who bowls occasionally in test matches, has 34 wickets in 50 tests.
West Indies coach Ottis Gibson said he backed the 30-year-old Shillingford to bounce back from his suspension.
"Though I felt confident about the way the two players performed at the testing, the report did not come back in our favor," Gibson said.
"Shane is obviously gutted but Marlon's role in the team, as I have said previously, is primarily as a batsman so the impact on him is a bit less.
"They are both tough characters and have had their share of ups and downs in the game over the years. We have no doubt that they will emerge from this latest setback with the utmost confidence."