Half a million Austrians have signed a petition calling for a smoking ban in bars and restaurants, embarrassing the ruling coalition of conservatives and far right that has championed both direct democracy and the right to smoke.

As part of their coalition pact, the far-right Freedom Party and Chancellor Sebastian Kurz's conservatives agreed to lift a smoking ban that is on the statute books and due to take effect in May. They also agreed to make it possible to call a referendum based on at least 900,000 signatures, but in 2022.

Doctors and an anti-cancer group decided to use one of the government's mantras against the other, organising an official petition within the current system that obligates parliament to consider an issue on the basis of 100,000 signatures.

That milestone was reached just three days after the petition was launched on Feb. 15 but the organisers have kept the initiative going as a show of strength against the government. It will run until April 4.

The government's bill lifting the impending ban is working its way through parliament and is expected to be passed by the lower house later this month.

"Five hundred thousand people have sent you a clear message: release your deputies from the party whip and make a free vote according to their conscience possible," the organisers of the petition said in a message to Kurz and Freedom Party leader Heinz-Christian Strache.

Kurz and Strache are unlikely to heed that call by the heads of Austria's main anti-cancer group and Vienna's doctors association. A government spokesman declined to comment.

Despite a trend towards banning smoking in the West, the Freedom Party sees a ban as restricting individual freedom and an unfair imposition on bar and restaurant owners.

On Tuesday lawmakers from the two ruling parties ensured the bill cleared the parliamentary health committee despite presentations by doctors who were called to testify by the Social Democrats and the liberal Neos party, which back a ban.

"No death is pleasant but dying of smoking is full of suffering," one of those doctors, Christoph Zielinski, told the committee on Tuesday.

"Respiratory distress, metastases in the brain, metastases in the bones - these are all awful. Passive smoking leads to this, too ... It is your responsibility. I ask you to reduce this human suffering as much as possible," he said.

A Unique survey of 500 people for weekly magazine Profil found that 71 percent of Austrians want a binding referendum on a smoking ban. The poll was published on March 3.