Below are notes from the usual source of annoyance.
Email from Expedia...
We’ve seen that there are a few dates where the rates at which your property is offered to travelers shopping and booking on Expedia Group websites are not competitive with those offered for your property on certain other platforms.
For instance, we noticed that on these dates, your property is offered on Booking.com with a lower rate citing an “early payment benefit”.
As part of our commitment to providing a traveler-centric marketplace, we conduct frequent reviews of pricing available to travelers. In order to maintain competitive offers for our travelers shopping and booking your property on our websites, we have decided to make these lower rates available to our travelers through our automated price matching technology.
Note that we are making these real-time and dynamic adjustments to ensure travelers shopping on our sites have access to competitive rates and offers by lowering our own compensation level for your bookings on our sites.
In the interest of transparency, we want to remind you that the compensation we receive for facilitating bookings is one of the factors influencing where properties appear in our search results. As a result, this lowered compensation level may have a negative impact on your visibility in our marketplace.
As Expedia Group wants to maintain a productive and trustful relationship with you and your property, we wanted to inform you of this initiative launched in reaction to one of our competitors’ activity. Should you have any questions, feel free to contact your market management team.

My response will make no difference but I did feel better sending it..

As you are well aware Booking.Com performs the same price cutting exercises as Expedia does. Like you price changes are made by all OTA’s by their own volition. I disagree completely at any OTA changing my advertised prices. OTA’s are making these real-time and dynamic adjustments without my knowledge or consent so I am bound by our contractual arrangement to have no control over the issue. I receive the same offensive notes from Booking.Com as your note reads today. I find myself as the meat in a sandwich, a David with two Goliaths exerting their might against me.
Respectfully,