Building a new runway at Heathrow would have an "unacceptable" impact on local communities and the environment, the Conservatives have said.
MPs have voted to support the government's controversial plans for a third runway at Heathrow, despite a rebellion by Labour backbenchers.
Opening a Commons debate on the plans to expand Heathrow, shadow transport secretary Theresa Villiers called for a "better, not bigger airport".
They rejected a Conservative motion calling for the £9bn scheme to be reconsidered, by 297 votes to 278 a majority of 19 votes.
Transport Secretary Geoff Hoon accused the Tories of "political opportunism".
Up to 40 Labour MPs had been expected to vote against the government.
Earlier, Labour MP Andrew Slaughter quit his government post to campaign against the proposal.
The Tories and Lib Dems oppose the plan but Labour says it will aid the economy and not breach environmental targets.
Mr Slaughter stepped down as an aide to Foreign Office minister Lord Malloch-Brown, saying he believed the £9bn project could still be blocked.
MPs are debating the controversial £9bn project and, despite an anticipated rebellion by up to 40 Labour MPs, ministers are believed to be expecting to win a vote, having made a number of concessions.
'Unconvincing'
Labour rebel Paul Flynn claimed government whips were piling pressure on the party's MPs and were even flying some of them back from Strasbourg, where they have been attending a Council of Europe plenary session, to vote for a third runway.
Mr Flynn - who accused the government of offering "flights for votes" - said those Labour MPs like himself who were returning from Strasbourg to vote against the government would not get their travel costs reimbursed. The decision by the Conservative policy [to oppose expansion] is political opportunism of the lowest kind Geoff Hoon, Transport Secretary
The Labour whips office confirmed some Labour MPs were flying back to vote, but refused to say how many or comment on Mr Flynn's claims that those who opposed the government would have to pay their own travel costs.
Ms Villiers said the Heathrow expansion would lead to an unacceptable increase in air and noise pollution.
She said proposed environmental safeguards did not "stand up to scrutiny" while the economic arguments for expansion were "wholly unconvincing".
'Dodgy'
The Tories had a "credible" plan to make Heathrow better, she added, with the construction of "viable" high-speed rail links relieving overcrowding at the airport.
But Mr Hoon said the Conservatives had failed to spell out criteria for acceptable limits for air and noise quality and that their arguments could not be "taken seriously".
Given the airport's importance as a global transport hub and current strains on its capacity, failure to expand Heathrow would do "serious damage to Britain's jobs and economy".
"The decision by the Conservative Party [to oppose expansion] is political opportunism of the lowest kind," he said.
This will go on until politicians pluck up the courage to say no and I think this is the moment to do so Chris Mullin
Lib Dem transport spokesman Norman Baker said the case for expansion was "dodgy" and there was "overwhelming opposition" to the plan.
The "massive" increase in flights being proposed could not be reconciled with the government's target of cutting carbon emissions by 80% by 2050, he added.
When it gave the go-ahead for the runway earlier this month, the government said it would impose tight conditions on further expansion to limit its environmental impact.
There will be a cap on the number of flights initially allowed to use the new runway and "green slots" will only be given to airlines with the newest, least-polluting aircraft.
But the development would result in the demolition of 750 homes and the disappearance of the village of Sipson.
Mr Slaughter, MP for Ealing, Acton and Shepherd's Bush, said he had quit his unpaid post - the lowest rung of the government ladder - to "continue campaigning" against the plan.
In a letter to his constituents, he said he had opposed airport expansion for 20 years.
"Ministers are insisting that stringent noise and pollution limits are met before the new runway can be used," he wrote.
"But Heathrow will seek a way to break these promises once again. Opposition from residents and green groups means that we can stop a third runway being built. I assure you that my fight against it will go on."
Vote anger
Ministers say a parliamentary vote on the new runway is not necessary, to the anger of many MPs.
But the Conservatives secured a debate as part of their opposition parliamentary time.
Although Wednesday's vote will not be binding on ministers, it would be embarrassing if they lose it.
Before the government gave the go-ahead for the new runway, more than 50 Labour backbenchers were among 132 MPs to sign a motion calling for the government to reject the idea.
One of those, former transport minister Chris Mullin, said the plan would "drive a coach and horses" through the government's policy to curb carbon emissions and would not satisfy the "aviation lobby" and its desire for expansion.
"This will go on until politicians pluck up the courage to say no and I think this is the moment to do so," he said.
But it is thought several MPs previously opposed will support the plan because of the concessions and the backing of cabinet ministers, such as Ed Miliband, previously thought to be sceptical.
Hugh Bayley, Labour MP for City of York, said the government had done "enough" to win him over but would only continue to command his support if it "vigorously" pursued plans for high-speed rail.
It is reported that a small number of Conservative MPs may rebel against their own leadership while the Democratic Unionist MPs are expected to support the government.
One of the few backbenchers to speak up for the runway, Labour MP Graham Stringer, said there was "no economic alternative" to the project.
Employers and union leaders say the runway will create thousands of jobs and ensure London remains competitive.
But a coalition of local councillors and environmental campaigners have vowed to mount a legal challenge, a move supported by Mayor of London Boris Johnson.
