The FIA will announce its decision regarding the alleged illegal tire test conducted by Mercedes AMG Petronas and Pirelli in Barcelona in May.

While Mercedes and Pirelli both defend the tire tests were completely within the regulations, appeals brought forth by Red Bull Racing and Ferrari suggest that both groups were testing under the radar, booking the test without other teams' knowledge and using blank driver helmets. The FIA also stated it had not granted official permission for the test.

In their defense, Mercedes claims they were working under Pirelli's guidance to help to solve the 2013 tire delamination problem, while Pirellii says they were conducting tests for 2014.

If punished, both groups could face heavy fines, point reductions or even Mercedes' race win in Monaco.

An official decision will be announced Friday.