A U.S. Armed Forces swearing in ceremony during a National Women's Soccer League match in Oregon on 9/11 drew loud boos from the crowd when the enlistees were asked to pledge allegiance to President Trump.

The ceremony took place in the middle of the field at Providence Park stadium in Portland on Wednesday night as a way to commemorate 9/11 during the Portland Thorns and North Carolina Courage game.

The group of enlistees were initially cheered on by the 17,000-strong crowd when they started taking the Oath of Enlistment.

The ceremony took place in the middle of the field at Providence Park stadium in Portland on Wednesday night as a way to commemorate 9/11 during the Portland Thorns and North Carolina Courage game

But the crowd quickly turned when the enlistees were asked to support Trump.

Loud boos rang out across the stadium when the group were asked to 'obey the orders of the President of the United States'.

Some fans slammed the league for allowing the military-swearing in to take place at the game given the fan code of conduct bans political signage at matches.

The Major League Soccer has come under fire of late following recent changes to its fan code of conduct.

Those changes include banning fans from displaying political banners within club stadiums.

An example of signage banned by the MLS is the Iron Front symbol showing three arrow pointing down.

The group of enlistees were initially cheered on by the 17,000-strong crowd when they started taking the Oath of Enlistment at Providence Park in Portland, Oregon

It was first used by anti-Nazi groups in Germany but the MLS has raised concerns about it being used now in the antifa movement.

Earlier this month, a Utah couple were banned from waving a Betsy Ross falg at a Real Salt Lake match.

Randolf and Diana Scott, who are season ticket holders for the Real Salt Lake team, said they were asked to take down their Betsy Ross flag during a recent home game match.

They claim staff at the stadium told them they would be kicked out if they didn't put away the Revolutionary War-era U.S. flag with 13 white stars in a circle.