David Lammy sparked a fresh row with a key trade union on Sunday by saying Labour should categorically refuse to back demands from airline workers for a pay rise of about 10%. Unite – which says staff are just asking to reverse a pay cut that occurred during the pandemic – accused the shadow foreign secretary of launching a “direct attack” on the workers it represents. The general secretary, Sharon Graham, said his comments were a “new low” for Labour, which could not be relied upon by working people. Graham has previously indicated she wanted to scale back Unite’s contributions to Labour. The union was once one of the party’s biggest donors, but Graham has repeatedly indicated she would like to divert its budget elsewhere. Labour has been criticised for not backing the RMT in the current dispute that triggered the rail strikes, but Lammy firmly dismissed airline workers’ pay demands in his interview on the BBC’s Sunday Morning show. Lammy was asked if he supported the BA check-in staff at Heathrow who have voted go to on strike over management’s refusal to reverse the 10% pay cut imposed during the pandemic and who are represented by Unite. “Many of us might want a rise of 10%,” Lammy said. “In truth, most people understand it’s unlikely that you’re going to get that.” Asked directly if he supported the check-in staff, who are members of Unite, Lammy replied: “No, I don’t. It’s a no. It’s a categorical no.” Asked why he would not support them, he replied: “Because I’m serious about the business of being in government, and the business of being in government is that you support negotiation.” Referring to the rail dispute, he said: “This government isn’t negotiating. This government is not supporting reaching a compromise.” In a statement issued on Sunday afternoon, Graham said: “David Lammy has chosen to launch a direct attack on British Airways workers. This is a group of workers who were savagely attacked by their employer during Covid.” Graham said that the workers were not asking for a 10% pay rise, but the restoration of money taken from them when pay was cut during the pandemic. BA and its parent company, IAG, had billions in reserves, and were predicting a return to profit this quarter, she said. She went on: “Supporting bad bosses is a new low for Labour and once again shows that politicians have failed. It is now down to the trade unions to defend working people. We are their only voice.” Last week Graham accused Keir Starmer of a failure of leadership after he ordered frontbenchers not to join RMT picket lines for the rail strike. “You don’t lead by hiding,” she said. Asked what would happen to the Labour MPs who did join picket lines to show their support for the RMT rail strike, Lammy said that Alan Campbell, the shadow chief whip, would be speaking to them “and making it very clear that a serious party of government does not join picket lines”. Some frontbenchers and parliamentary aides were among those picketing, even though they had been explicitly ordered to stay away by Starmer’s office. Lammy said Labour was the party of working people, but that did not mean it should automatically side with workers against employers in a dispute. Although rail workers had legitimate grievances, he suggested, there were also “working people who use the trains to get to work”. On Tuesday, the Communication Workers Union is due to start balloting postal workers on strike action over a pay rise offer of 2%. Dave Ward, the CWU general secretary, told Sky News on Sunday that he was “disappointed” by Labour’s attitude towards unions taking industrial action. “I think Labour have miscalculated, because I think they’re obsessed with reconnecting with working people, and the reason that people moved away from Labour was over Brexit,” he said. “I don’t think people are going to turn their backs on working people who are facing these challenges because we’re all genuinely in that together.”