John Gill Commentary Esther 3:3

"Then the king`s servants, that were in the king`s gate, said unto Mordecai, Why transgressest thou the king`s commandment?" — Esther 3:3 (ASV)

Then the king's servants, which were in the king's gate
Observing the behaviour of Mordecai towards Haman from time to time:

said unto Mordecai, why you transgress the king's commandment ?
of giving reverence to Haman, which they knew he could not be ignorant of.