The Pledge of Allegiance is an oath that young American children are forced to say every day in school. It is criticized for being xenophobic, and it does violate the Free Establishment Clause of the 1st Amendment to the Constitution. The words, ever since 1954 are:
I pledge allegiance, to the flag, of the United States of America,
and to the Republic, for which it stands;
one nation, under God, indivisible;
with liberty and justice for all.
The version in plain English is:
I am giving up past loyalties to other nations, and I shall change it to the flag of the US, and to the nation too;
unified as one, under one god,
never seperated by race, culture, heritage, religion, etc.
with freedom and justice for all.
The reason why the pledge is controversial, is because it removes a man of many nations, and also says there is one god, and one god only. Polytheists, animists, atheists, etc. are offended. Even Jehovah's Witnesses see this as flag worship and they don't believe in voting!
Liberty and justice for all would be good if it happened but rich Americans have more freedom than poor Americans. Further rich Americans can afford better lawyers and the justice system is likely to favor them.
Some school students can opt out of the pledge but others can't.  In at least one area there is discussion about extending freedom to opt out.  Even if an opt out is allowed officially pressure from teachers and peers may make it hard for students actually to opt out. In some states, there is no law regarding the pledge. The laws by state also affect private schools, because they are in the state, and therefore under jurisdiction of the state.