Yes, this will happen if the last names don't match. Or other items may trigger this. It is a credit card fraud protection policy.

The card owner can go to an United Counter and present the card and have a comment place in the reservation record authorizing the usage -- I have done this.

Another approach that has been reported is a signed letter but no guarantee this will be accepted.

A phone call probably will not work.

It has also been reported that this is not always checked. YMMV