In qualifying later today, it'll be important for teams to put on the medium compound tyre in Q2. This is because the tyres the drivers set the fastest time on Q2 will become the starting tyres for the race and they can, therefore, have a longer stint at the start of the race. From the 2020 Formula 1 season, the FIA wants to remove the rule but it requires a team vote first.
The rule change proposal has been submitted to the teams. The change would mean the top 10 drivers are no longer forced to start on the tyres which they set the fastest lap on in Q2. The vote requires all teams to agree.
The rule was created in the hope that it would create a mix-up. (The top ten would drive on a softer compound and have a disadvantage at the beginning of the GP itself because they'd be forced to change earlier.