Asthma inhaler maker Vectura has been excluded from a pharmaceutical conference after academics staged a rebellion over the company’s £1.1bn takeover by cigarette company Philip Morris International (PMI).

PMI effectively sealed the takeover on Thursday, after more than half of Vectura’s shareholders agreed to sell their stock.

But within hours the deal was overshadowed by the removal of Vectura as a sponsor of, and participant in, a conference called Formulation and Delivery UK due to take place next week.

Emails seen by the Guardian show that a group of leading clinicians who were invited to the event objected to Vectura’s involvement because of its links to PMI, which says it is aiming for a “smoke-free future” but still derives 75% of its revenue from selling cigarettes.

Peter Barnes, professor of thoracic medicine at the National Heart and Lung Institute, coordinated a letter from multiple academics to event organiser Oxford Global, describing the takeover as “extremely unwelcome news”.

“Unless the sponsorship and invitation to Vectura to participate is withdrawn, we will no longer be able to take part in the conference next week and will have to withdraw from the programme,” he said.

Further correspondence shows that Oxford Global later confirmed that Vectura “will no longer be participating in or sponsoring the event”.

Barnes said he expected other pharmaceutical industry events would follow suit because professional societies for specialist respiratory scientists and clinicians did not allow them to participate in any events with links to the tobacco industry.

Vectura’s removal from the conference appears to lend weight to warnings from academics that the company could be prevented from working with leading scientists in its field, respiratory medicine. Vectura declined to comment. The Guardian has approached PMI for comment.

PMI wrapped up the Vectura deal on Thursday morning, saying it had either bought shares, or received acceptances of its offer, reaching just under 75% of the company, well ahead of the 50% it needed.

The offer has become “unconditional”, meaning the remaining shareholders cannot prevent it and can in effect be compelled to sell.

The takeover of a respiratory disease specialist by a cigarette company has sparked outrage among health charities and public health experts around the world.

But the Marlboro maker has argued that its transition away from cigarettes requires it to move into fields such as respiratory medicine, where it already has some expertise.

Jacek Olczak, the chief executive of PMI, said on Thursday: “We are very excited about the critical role Vectura will play in our beyond nicotine strategy and look forward to working with Vectura’s scientists and providing them with the resources and expertise to grow their business to help us achieve our goal of generating at least $1bn [£725m] in net revenues from beyond nicotine products by 2025.”

Vectura investors had been given until 15 September to decide whether to sell to PMI. Under market rules governing takeovers, PMI was not allowed to build its stake by buying shares from investors within the US.

But it was able to buy stock from other international investors to move closer to its 50% target. It said in August that it had gathered 29% of the stock, as it sought to reach 50%.

At that point, which PMI has now reached, reluctant shareholders have little incentive to hold out because PMI would take control of the company anyway. PMI said on Thursday morning that investors could still sell their shares to it until 30 September.

Sarah Woolnough, the chief executive of Asthma UK and the British Lung Foundation, said: “There’s now a very real risk that Vectura’s deal with big tobacco will lead to the cigarette industry wielding undue influence on UK health policy.”