The policy change comes after passenger Dr. David Dao was dragged off a flight and left bloodied when he did not give up his seat for a crew member.
The airline, owned by United Continental Holdings, said on Friday that it would make sure crew travelling on its aircraft are booked into seats at least 60 minutes before departure. Adding that the change is "one of our initial steps in a review of our policies in order to deliver the best customer experience".
United spokeswoman Maggie Schmerin said in an email that the new policy is meant to ensure that such incidents will "never happen again".
The dragging has turned into a public-relations nightmare for the entire industry, not just United, and led to calls from politicians and consumer advocates to suspend or ban overbooking.
United had selected Dao and three other passengers at random for removal from the plane after unsuccessfully offering the vouchers and a hotel stay to customers willing to give up their seats.
A man on board a United flight on Sunday from Houston to Canada said a scorpion dropped on his head from an overhead storage bin and stung him under his fingernail, according to United and media reports.More news: Police Searching For Two Teenagers And A Three-Day Old Baby
If you have access to the internet, then you have undoubtedly heard about - or likely seen - the highly disturbing footage of a United Airlines customer being forcibly dragged off a flight this week. His lawyer Thomas Demetrio said David Dao suffered a concussion, a broken nose, and lost two teeth. The airline also promised to no longer ask the police to remove any passenger from full flights.
He said a lawsuit would be filed against the airlines soon. Later, Munoz offered a more emphatic mea culpa, saying: "No one should ever be mistreated this way".
Members of the U.S. Congress have also expressed concern, as U.S. House Representative Judy Chu, a Chinese American, has written both to the United Airlines and to the U.S. Department of Transportation demanding answers.
The department's roughly 300 officers guard the city's two main airports but are not part of the regular Chicago police force, receive less training and can not carry guns inside the terminals.
Linda said United reached out to her husband Wednesday to apologise and to offer compensation for the incident. But the airline later said it needed to make room for its own employees to keep other flights on schedule.