Supermarket supplies could be hit as warehouse workers threaten to go on strike amid claims managers are trying to take advantage of the pandemic to employ "union busting" tactics.

The Unite union is asking 350 members at the Sainsbury's distribution warehouse in Dartford, which is operated by DHL and employs the staff, to consider walking out.

It follows claims the logistics giant is ignoring workers' concerns and was triggered by the "completely unjustified" suspension of a union representative at the DHL site, Unite regional officer Phil Silkstone said.

He said the representative was challenging a manager during an investigation hearing and became aggressive which Unite says has been contradicted by an independent witness at the meeting.

The union says it is the latest incident across the country leading it to accuse DHL of using the "uncertainty of the pandemic" to carry out an "anti-union agenda".

Sainsbury's – which is not involved in the dispute – says it is preparing contingency plans to prevent disruption to the supply chain at the warehouse which is used as a regional distribution depot for stores across the south east.

Mr Silkstone said: "DHL lorry drivers, clerks and warehouse operatives at Sainsbury’s Dartford warehouse are being balloted for industrial action. This is in response to the completely unjustified suspension of a Unite steward for representing a staff member.

“The baseless accusation of aggression by a single manager used to carry out the suspension has been flatly contradicted by a neutral staff member who was present at the meeting. Unfortunately, the suspension is the not the first instance at the Sainsbury’s site where union members have been targeted.

“An attack on one is an attack on all and our DHL Dartford members are keenly aware that should this be allowed to stand it will herald further attempts to erode employment standards and worker protections at the site.

“Sainsbury’s will not be pleased to learn they are facing potential disruption to their supply chain in the run up to the Easter period, which will affect the availability of chocolate eggs and other Easter provisions, because of DHL’s anti-union agenda.

“Unite would much prefer an amicable relationship with DHL and does not want to witness empty shelves at Sainsbury’s stores, so we urge the company to see sense, get around the table and revoke this unfounded suspension.”

A spokesman for DHL Supply Chain said the company is "disappointed" about the threat of strike action at the site off Rennie Drive in the shadow of the Dartford Crossing.

They added: "As ever, we remain willing to work with the union to reach a satisfactory outcome for both parties, but contingency plans are being drawn up to minimise any impact on deliveries should the action go ahead.”

Unite has claimed a "recent change in management structure" at DHL has caused difficulties for workers.

National officer Matt Draper said there had been many "worrying incidents" at DHL sites including Liverpool, Halewood on Merseyside and Solihull in the West Midlands.

He added: "Before this recent trend of attempted union busting, Unite had, on the whole, a constructive relationship with DHL.

"We believe the breakdown in industrial relations is due to a new approach by management, who seem to be testing the waters during the uncertainty of the pandemic to see if union activity, and the protections it affords to staff, can be weakened."

It is feared this could lead to lesser pay and conditions for staff and Mr Draper said DHL needed to "press reset" to return to previous working relationships.

A Sainsbury’s spokesman said: “We are monitoring the situation very closely and encourage both sides to keep talking.

"We can reassure customers that we have contingency plans in place to minimise any disruption this may cause.”

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