Christian campaigners in Salford are accusing supermarket giant Sainsbury's of heavy-handedness after they were threatened with police action unless they moved on.

The seven protesters, who included three clergy, picketed the Salford branch of Sainsbury's on Saturday as part of a campaign against the chain's pilot of a replacement of the Fairtrade mark on its tea with its own 'Fairly traded' brand.

One of them, Hilary Thomas, told Christian Today that Christian Aid North West co-ordinator Ruth Platt had contacted the store previously and had been told there 'would not be a problem' with the protest.

'The manager came out and greeted us politely and explained Sainsbury's position,' Thomas said.

'She then came out again looking worried and said she had had instructions from head office and that we had to move, and if we didn't comply she would call the police.

'It felt quite heavy-handed, to say the least.'

She said the group had collected around 60 signatures to a petition objecting to Sainsbury's new scheme, which she described as 'confusing' to consumers.

The Fairtrade scheme allows farmers to decide for themselves how the 'social premium' – the extra profit on goods designed to benefit the whole community – is spent, whereas under Sainsbury's' own-brand scheme the supermarket will control how the money is spent. Thomas told Christian Today Sainsbury's' own 'Fairly Traded' scheme 'looks like colonialism'.

Sainsbury's faced protests at its annual meeting in London in July, with shareholders objecting to the move. Anne Lindsay, a private-sector analyst from Cafod, the Catholic charity, said to the board: 'I am concerned that after years of being an extremely valuable champion of Fairtrade, Sainsbury's is starting in a direction that could undermine Fairtrade and lead to a plethora of different standards by different companies and confusion for consumers.'

Also among those expressing concern at the move is Tearfund, which in a briefing paper encouraging people to protest quoted an open letter from producers saying: 'We see the proposed approach as an attempt to replace the autonomous role which Fairtrade brings and replace it with a model which no longer balances the power between producers and buyers.'

Sainsbury's says on its website it will 'continue to test and trial our new approach, listening and learning as we go' and that it is committed to transparency.

Asked about its reaction to the Salford protest, a spokeswoman told Christian Today: 'I can confirm the police were not called and the protestors even popped into the café for a cup of tea after they'd collected signatures.'