Discount supermarket chain Aldi is selling pairs of replica Eames chairs for £39.99 – a fraction of the £339 it costs to buy a single authorised version of the chair.

Aldi is advertising "a pair of retro-style Eiffel chairs" on its website in the UK for £39.99 – the latest in a string of replica designs sold at heavy discounts by the budget supermarket chain.

The Eiffel chairs are almost identical in appearance to the DSW Eames Plastic Chair, designed by Charles and Ray Eames in 1950 and produced under license by Swiss design brand Vitra.

The similarity between the designs has been flagged on social media, with furniture designer Rupert Blanchard sharing images of the Aldi version of the chairs from one of its stores in London.

Blanchard's image was accompanied by the comment: "@AldiUK is selling #fake #Eames #eiffel chairs, not cool Aldi, not cool."

He also shared an image of the packaging, which shows that the Eiffel chairs are made in China.

Aldi replied to Blanchard via its Twitter account, writing "We're sorry to hear that you feel this way and rest assured we will share your feedback with the relevant team!"

Sit Down Protest:@AldiUK is selling #fake #Eames #eiffel chairs, not cool Aldi, not cool. pic.twitter.com/ESX0f4rEEW

— Rupert Blanchard (@RupertBlanchard) June 1, 2016

In a one-line statement sent to Dezeen, Aldi said it was not infringing on copyright.

"Our retro-style Eiffel chair does not infringe any design rights," it said. The company did not provide any further comment. Vitra declined to comment.

Oliver Wainwright, architecture and design critic at the Guardian newspaper, defended Aldi on Twitter. "Isn't this exactly what Charles Eames would have wanted?" he tweeted. "The licensing model that sees Eames designs elevated to luxury collectibles goes utterly against everything they stood for."

He added: "If a licensed original costs £333 and a pair of copies is £39.99, I think Charles Eames would tear that license right up".

It is not the first time the global supermarket chain has offered imitations of the Eames' designs. It has also sold replicas of Mies van der Rohe and Lilly Reich's Barcelona Chair and Philippe Starck's Ghost Chair at stores in countries like Australia, where copyright law allows copies to be sold as long as they are clearly labelled as a replicas.

Aldi is not alone in selling replicas of the DSW chair – amongst many others, Tesco is currently advertising a Charles Eames Inspired Eiffel DSW Dining Chair for £49.99 – but it is one of the cheapest.

Under current UK law, it is legal for Aldi to sell replicas of well-known design classics, as copyright law only covers industrial designs for a period of 25 years after they are first marketed.

However, new copyright legislation will come into effect this summer, under the repeal of section 52 of the Copyright, Designs and Patent Act 1988, extending the copyright period to 70 years from the designer's death.

The DSW Eames Plastic Chair, which was launched onto the market in 1950, is one of many items of designer furniture that will be newly protected.

The chair was the result of the Eames' mission to create more accessible design. The single-piece shell was originally moulded from glass-fibre reinforced polyester resin – according to Vitra, this enabled them to create the first mass-produced plastic chair.

Vitra now makes the design in polypropylene plastic, which is the same material Aldi says is used for its Eiffel Chairs.

The shell of the Eames' chair can also be combined with different bases. The so-called Eiffel Tower base consists of a structure of metal rods, and is echoed in a wooden version with tapered legs connected by criss-crossing metal supports. The latter is the version that has been mimicked by Aldi.

The section 52 repeal comes into force on 28 July 2016. From 28 January 2017, all dealers will be required to have disposed of all replicas or unauthorised copies – meaning they can continue to sell existing stock until then.

The change is a result of 2013 reforms to bring UK copyright law in line with the European Union, which has longer-lasting protections for artistic works.

The appropriate length of amnesty for retailers to adjust to the reforms by clearing already produced stock was the subject of heated debate.

A coalition of design brands including Vitra, Artek and Flos joined forces to lobby the government after learning that the law would not be brought into effect until 2018.

"The UK has never had the same level of intellectual property protection as the rest of Europe," Tony Ash – managing director of Vitra in the UK, USA, India, Middle East and Far East – said at the time.

Ash claimed the anomaly meant the UK had become "a laughing stock" and told Dezeen "The UK has become a Trojan Horse for the importation of copies into Europe".

Charles and Ray Eames' grandson Eames Demetrios, who runs the Eames Office set up by his grandparents in Los Angeles, told Dezeen last year that developments in the music industry were partly to blame for the proliferation of designer furniture replicas.

"I think the music industry hasn't done anybody any favours by adopting the approach that it did," he said.

"If you had to ask your grandfather in 1950 to make a copy of a chair he would have said 'okay but it'll take me a week'. Now if you asked someone, the image in their mind of copying is to drag a file from one side of the desktop to another. They think of everything as cloneable."