Gary,
That is different than a residential fixture, but the idea is the same. It is as good as the change in daylight savings time and ethanol in motor fuel. It was part of the same congressional energy saving. It is supposed to limit the flow of a shower to 1.5 GPM. But there is a problem and frequently the rubber plug that is supposed to deform and maintain that flow gets deformed and does as yours is.
You might be able to pull that plug out and replace it or the fitting. You can't leave it out because that would be defying a congressional edict.
Matt