The newly-formed group in Elmbridge, Surrey, called Rage, is opposing flight path changes and expansion.
Campaigners said Dominic Raab MP had not set out his views and were shocked that Elmbridge council had only just formed a task force.
Both the council and MP said they had not yet reached an official view.
The Esher and Walton Conservative MP said on his blog he was scrutinising the report by the Airports Commission, looking at the economic and environmental assumptions, testing assumptions on noise levels, and checking facts and evidence before reaching a firm view.
In a statement, Elmbridge council said it agreed in September to set up a group to explore the impact of Heathrow expansion and the outcome would inform its view.
Rage spokeswoman Katy Glassborow said expansion would bring more noise and pollution.
She said: "It's about time he [Dominic Raab MP] found out what local people think and showed his colours on their behalf.
"We are calling on him and also Elmbridge Borough Council to move quickly to represent our views and oppose expansion plans.
"Otherwise, hundreds of thousands more planes could be flying over our homes and schools."
Heathrow has said it is reducing its noise footprint and insisted that its air quality is better than the rest of London.
In July, the Airports Commission backed plans to build a new third runway at Heathrow, after nearly three years of deliberation.
The government has said it expects to make a decision by the end of the year.
Campaigners fighting Heathrow expansion have demanded their MP and council take a stance on the issue - as a government decision looms by the end of the year.