The commission claimed Eurotunnel, which now runs 16 ferry crossings a day, bought the boats to prevent Danish rival DFDS from picking them up cheaply and driving down prices.
But DFDS Seaways has warned of potential disruption and said it was not taking any new bookings for its Dover to Calais and Dover to Dunkirk services during the proposed strike period.
The tree, which is usually 20 to 25 m (70 ft) in height and anything between 50 and 60 years old, is then shipped free-of-charge across the North Sea to Immingham by DFDS Tor Line.