Twenty MSPs from across the political divide signed a parliamentary motion that called Historic Scotland's lack of opposition regrettable. They said it was imperative the country protects its history.
The political support will be seen as a victory for the protest group Save Our Landscapes, which has opposed the plans on grounds they will harm the environment and contradict previous Government promises.
South Lanarkshire Council is considering a proposal by global cement company Cemex to extend its Hyndford Quarry into the buffer zone around New Lanark, adjacent to the historic viewpoint overlooking the Falls of Clyde.
The falls have inspired generations of poets and painters, including William Wordsworth and JMW Turner, while 18th-century New Lanark was made famous as the setting for Robert Owen's model of utopian Socialism.
The proposed expansion would result in the lowering of the landscape by 100ft in places, with 3.6 million tonnes of sand and gravel extracted from the area over six years.
The council's planning committee is expected to make a decision in April.
Joan McAlpine MSP, who tabled the motion, said: "Like most visitors, I like to go walking in the surrounding countryside that provides a stunning setting for New Lanark. One of the attractions of the village and living museum is its beautiful natural setting. I don't think you can separate the two."
She praised the man heading up Save Our Landscapes, Professor Mark Stephens, and suggested Historic Scotland was wrong to find the huge quarry would have no significant impact on the setting of New Lanark.
She said: "Professor Stephens has made a very good case against the potential destruction of the designed landscape by the quarry. I have not been satisfied with Historic Scotland's justification for failing to oppose the development.
"This is a World Heritage Site of which we should be very proud. Scotland has an excellent global reputation for conserving both our natural and built heritage and we shouldn't do anything to damage that reputation."
Protesters have been angered by Historic Scotland's apparent change of heart after the agency nominated New Lanark for World Heritage status in 2000 in a move signed off by the then first minister, Donald Dewar.
Their anger turned to disbelief last week when it was revealed Historic Scotland had mistakenly referred to the quarry as a wind farm in an internal document.
Nearly 7000 people in 45 countries sign the petition, organised by Save Our Landscapes, opposing the quarry.
And the group has collected 2000 letters of objection covering every postcode in the council area.
Mr Stephens said: "It is important for MSPs to signal that, where you have an area that enjoys nationally and internationally important designations, those designations should be upheld."
Historic Scotland said: "We are aware of the motion and have already arranged to meet Ms McAlpine to discuss our role in the consultation process."
Cemex said that throughout any planning procedure it had consulted with all stakeholders, including Historic Scotland.