A coalition of trade unions and predominantly European clothing retailers have agreed to a legally binding plan to inspect garment supply factories in Bangladesh within nine months.

The 75 signatories to the accord, unveiled on Monday, will guarantee that in every case where unsafe conditions are found, funds will be made available for necessary safety upgrades.

But only three US retailers have signed up to the plan. American firms are reportedly reluctant to join any industry accord that creates legally binding objectives. The small number of US signatories will disappoint advocates hoping for an end to dangerous conditions in Bangladesh's multi-million pound garment industry, in which 1,200 people have died in the past year.

A push for western retailers to take more responsibility for workers' conditions in Bangladesh came after a series of recent tragedies, such as the Rana Plaza building collapse outside Dhaka in April, which left more than 1,100 dead, and the Tazreen factory fire in November that left 112 garment workers dead. Labels for US and European brands were found in the rubble of the factories.

Some retailers, such as Primark, the British retailer and Loblaw, the Canadian company that makes Joe Fresh, confirmed soon after the tragedies that the Rana Plaza factory made their clothes. Primark and Loblaw have now signed up to the safety accord.

Negotiations between unions and retailers began in May, in the aftermath of the Rana Plaza deaths. Signatories also include H&M, one of Bangladesh's biggest clothing clients, Marks & Spencer, and at least three US companies: Abercrombie and Fitch, PVH, the parent company of Calvin Klein and Tommy Hilfiger, and Sean John.

To allow for inspections, the western retailers have agreed to make public by 15 July a list of more than 1,000 names and addresses of Bangladeshi factories they use. International teams of fire and building safety inspectors, working with inspectors in Bangladesh, will inspect all the signatories supply factories within nine months to identify "grave hazards" and the need for "urgent repairs".

The failure of more US retailers to join the Accord on Fire and Building Safety in Bangladesh has led to criticism from unions and human rights groups. They say the European-led plan will make factories safer.

However, leading North American retailers, including Walmart, will come together on Wednesday to announce details of a rival plan: the Alliance for Bangladesh Worker Safety. Documents found in the rubble of the Tazreen factory showed that garment users supplying goods to Walmart and Sears were using the plant at the time of the fire. However, Walmart and Sears said they had no idea their clothes were being made at the factory.

The North American initiative was developed through a process facilitated by US senators George Mitchell and Olympia Snowe.

Christy Hoffman, the deputy general of UNI Global Union, said that the brands would require the factories to come up to certain standards and, when they do not, they would help to pay to bring them up to scratch.

Hoffman said it was "unfortunate" that more US brands have not joined. She said: "We have 75 brands signed up to this accord and we will be prepared to move forward without the US."

She said that joining the accord would cause a "very, very small increase" in the price of garments, "something like 2¢ per T-shirt".

"That is what it costs to make things safe in Bangladesh."

Jyrki Raina, the general secretary of the IndustriALL global union, said: "This historic accord will effect tangible change on the ground and help make the Bangladeshi garment industry safe and sustainable. Voluntary initiatives have proved insufficient, as 1,800 Bangladeshi garment workers have died in factory fires and building collapses during the past seven years."

Raina said that a "profound change" needed was only possible with a strong coalition between trade unions, international brands and retailers and Bangladeshi authorities with worker involvement.

A central aspect to the Accord, which is supported by the Workers Rights Consortium and the NGS Clean Clothes Campaign, is that it involved workers and their representatives. It also commits signatories to staying in Bangladesh for at least two years of the accord.

Critics have suggested that US companies were concerned over the cost of the plan.

Kevin Gardner of Walmart told the Guardian, in an email said that it had "taken a number of actions that meet or exceed other factory safety proposals" including strengthening safety standards, a "zero tolerance of unauthorised subcontracting" and "in-depth safety audits and remediations" made to every factory directly making its products.

Gardner said that Walmart was part of an alliance of retailers, industry associations and the Bipartisan Police Center, which was looking a the issue and would release details of their safety plan on Wednesday.

"What happened at the Tazreen and Rana Plaza factories is tragic." he said. "We are saddened by this situation and are working every day to improve worker safety in Bangladesh. Over the past several months we've taken a number of actions that meet or exceed other factory safety proposals and put out a lot of information on our audit process."