Workers are to take a day of action as part of a campaign aimed at ending the growing number of disputes over so-called “fire and rehire” tactics.
Unite said current strikes over the issue will be co-ordinated on Monday, and solidarity action will be taken at workplaces across the country.
Workers taking strike action on Monday will include bus drivers in Manchester, who are involved in a long-running dispute over pay and conditions.
Unite general secretary Len McCluskey said fire and rehire forces workers to accept worse pay and conditions in order to keep their job, describing it as a “disease” ripping through workplaces.
Research by the TUC suggested that one in 10 workers had been threatened with fire and rehire during the pandemic.
Unite warned that number will increase dramatically as furlough ends unless the law is changed to make the practice illegal, as it is in Ireland and Spain.
Howard Beckett, Unite’s assistant general secretary, said: “Millions of people all over the country are facing the sack if they don’t accept less pay and worse conditions.
“This wave of despicable fire and rehire tactics from bad bosses will only grow as furlough comes to an end. After months of pandemic hardship, this is no way to treat people.
“The Government knows this is wrong and can end fire and rehire. Businesses have been supported in the pandemic. Workers should be treated fairly too.
“We have members in every sector and in every nation taking industrial action, we have a strike fund of over £40 million and daily strike pay of £70. Fire and rehire will be stopped.”
Andy McDonald, shadow secretary of state for employment rights, said: “Boris Johnson and his ministers can’t continue to stick their fingers in their ears to avoid hearing story after story of bullying and abusive fire and rehire tactics.
“More and more companies – many that are making a healthy profit and have received financial support from the public during the pandemic – are treating their workers in this disgraceful way.
“The Government can and must act now by bringing forward legislation to end fire and rehire once and for all.”