Workers from across the country are to join a protest against the Government's controversial Bill on strikes and union activities.
The TUC will warn that the Trade Union Bill risks setting industrial relations back decades.
The Bill, which sets a new threshold for strike ballots and allows agency staff to be hired during industrial action, has been described as the biggest attack on unions in a generation.
New restrictions would be imposed on picketing and the posting of information on social media during industrial disputes, while 50% of union members eligible to vote would have to take part in a ballot for the outcome to be lawful.
MPs will be lobbied to oppose the Bill today ahead of its third reading in the Commons.
TUC general secretary Frances O'Grady will tell a rally in Westminster: "Working people from across the UK - midwives, steel-workers, dinner ladies - are travelling to London to show their opposition to the Trade Union Bill.
"I urge all MPs to listen to their concerns. The Trade Union Bill is an affront to all fair-minded democrats and a fundamental attack on the right to strike.
"In a year when we celebrate the 800th anniversary of Magna Carta, the Government is looking to take uncivil liberties with our basic freedoms.
"This Bill is both undemocratic and a threat to public safety. Because how can it be fair to fine unions up to £20,000 if they don't give two weeks' notice about what they are going to put on Twitter and Facebook during a strike?
"And how can it be safe to allow untrained agency workers to be used to break strikes?
"Good employers agree that instead of picking a fight with six million workers ministers should be focused on building a stronger economy that delivers better jobs and wages for all."
The TUC has launched a new advertising campaign about protecting the right to strike which will feature on billboards, motorway screens, at London Underground stations and at train stations across the country.
The campaign features workers - including a midwife, a firefighter and a cinema worker - who have "reluctantly" taken strike action in recent years.
Speakers at the rally will include Ms O'Grady, director of Liberty Shami Chakrabarti, comedian and writer Andy Parsons, workers who have taken strike action and trade union chiefs.
Matt Wrack, general secretary of the Fire Brigades Union, said: "We will campaign vigorously until this disgusting Bill is seen for what it is - the attempted removal of the rights of hard working people."
Claire Sullivan, the Chartered Society of Physiotherapy's director of employment relations, said: "The Trade Union Bill is a regressive piece of legislation that will affect not only the right to strike but will undermine effective negotiations between workers and employers around pay and working conditions.
"This Bill has been criticised by the police, business, NHS managers and politicians from across the political spectrum.
"If the Government really was interested in democracy at work as they claim, it would introduce electronic and secure workplace balloting."
Unison general secretary Dave Prentis will tell the rally: "This hard line bill attacks every worker in this country - union member or not. It's a bill that is stuck in the past, outdated and not fit for purpose.
"The Tories say they are the party of the working people but their bill attacks collective bargaining, attacks the work our reps do when they speak up for members, negotiate for fairness, for fair pay, for decency and for a better life at work.
"We are here today to deliver a message to this government.
"We are here to tell ministers that if trade unionism didn't exist, it would be born again."
A Department for Business, Innovation & Skills spokesman said: "People have the right to know that the services on which they and their families rely will not be disrupted at short notice by strikes supported by a small proportion of union members.
"The ability to strike is important but it is only fair that there should be a balance between the interests of union members and the needs of people who depend on their services."