Brentford, Bristol City and Ipswich have all been reminded about their obligations regarding the integrity of the Championship.
Huddersfield have come under fire from Blackburn and Nottingham Forest after making 10 changes in their 2-0 defeat to Birmingham.
All three sides could still go down on the final day but Forest boss Mark Warburton and Rovers counterpart Tony Mowbray were unhappy with David Wagner changing his team so drastically against their relegation rivals.
The Terriers have been asked for their observations and reasons for naming the side they did and the league have reminded all their clubs regarding a commitment to name the strongest possible side.
An EFL statement read: “Elsewhere last weekend, we saw Huddersfield Town make wholesale changes to their team that played Birmingham City.
“It is very much a subjective matter to determine what constitutes a ‘full strength’ side, however the disappointment of both Blackburn Rovers and Nottingham Forest is understandable.
“Huddersfield have been asked for their observations and reasons for taking the approach that they did.
“This type of approach is another challenge to the integrity of the competition, albeit a different one to the actions of supporters. We have reminded all clubs this week as to their obligations in this area.”
Brentford face Blackburn with Nottingham Forest hosting Ipswich. Birmingham, meanwhile, travel to Bristol City.