New Delhi, December 20 The Centre on Sunday wrote to the protesting farm unions, inviting them for the next round of talks and asking them to choose a date. In a letter to the union leaders, Agriculture Ministry Joint Secretary Vivek Aggarwal wrote, “I request those previously invited protesting union leaders to provide details of their remaining concerns and doubts and suggest a date as per convenience for the next round of talks.” The earlier five rounds of formal talks between the government and 40 farmers’ unions failed to break the impasse, with the farmers insisting that the Centre’s recent farm laws be repealed.