We want to add a dimmer to LED light fixtures on a single circuit.

An electrician states the dimmer cannot simply be wired into the light switch panel. Each fixture must be individually wired to the dimmer switch.

Is he correct, or is he trying to inflate the contract?

Thanks.

The only reliable way to tell how an LED light source will behave when dimmed is to actually test it. Otherwise, you might be in for an unpleasant surprise. But to be accurate, such testing should include the whole circuit, not just a single LED source with a single dimmer — because all dimmers have a minimum and a maximum number of LED sources they can effectively operate, and these limits can vary with the make and model of the LED source, the remote driver (where applicable), the dimmer, and (for low-voltage systems) the transformer. What’s more, variations in any part of the system can affect dimming performance, which means that substituting a different lamp, driver, transformer, or dimmer for what was originally specified can lead to dimming problems. Try it with 1 dimmer and see how it works. One issue is that the load for LED's (very low) can make the dimmers not function properly.