Her year-long battle with striking miners in 1984/5 typified her confrontational attitude to the union movement and her victory paved the way for a radical shift in the balance of power in industrial relations.
The Conservative government introduced eight employment-related acts between 1970 and 1990 which all hit union power.
Mass picketing was outlawed, ballots had to be held before industrial action could be taken, secondary action was made illegal and union leaders had to face regular elections to keep their jobs.
Prime Minister Thatcher was given strong support by senior colleagues including Lord Tebbit, who described striking workers as "bully boys" and "wreckers".
Baroness Thatcher partly earned her nickname of the Iron Lady because of the way she took on once-mighty union leaders.
She infuriated the labour movement by banning union membership at the GCHQ communications centre in Cheltenham in 1984.
The legislation was introduced gradually throughout the 1980s, leaving unions weaker and managers stronger.
The number of working days lost through industrial action slumped from 29 million in 1979, falling to record low levels of less than half a million by the end of the 1990s.
The introduction of so many new laws was central to the Conservative government's philosophy of making unions more accountable, ending strikes, deregulating industries and "freeing up" the economy from constraints.
Margaret Thatcher oversaw a sea change in government policies, industrial relations and the balance of power in the workplace.
She killed off the previous tripartite relationship between unions, employers and government.
Beer and sandwiches in 10 Downing Street were confined to history as unions were excluded from policy making and left to protest on the sidelines.
The attack on unions followed the defeat of Edward Heath's government in 1974 after failing to take on the miners, and the Winter of Discontent, which saw a series of strikes by railway workers, Ford car employees, petrol tanker drivers and local authority workers including gravediggers.
Margaret Thatcher emerged as Tory leader during these events, determined to demand greater accountability from trade unions.
Legislation included Employment Acts in 1980, 1982, 1988, 1989 and 1990 and a Trade Union Act in 1984.
Unions were in constant conflict with the Conservative regime during the 1980s and the chant "Maggie, Maggie, Maggie. Out, Out, Out" became a well-used anthem at countless marches and rallies.
Union membership fell from more than 12 million in 1979 to 10 million a decade later.
But stronger and more militant unions came into conflict with the legislation and there were violent clashes on picket lines, including one mounted by the National Graphical Association in Warrington where the union was trying to enforce a closed shop at a printing works.
The union was heavily fined and had its assets sequestrated and a national newspaper strike supported by the TUC was declared illegal.
The miners' strike of 1984/85 was the biggest test of the legislation, and the biggest union clash she faced during her time as prime minister.
Job losses and pit closures sparked the dispute, but NUM leader Arthur Scargill decided not to hold a national ballot and the year was dominated by mass picketing, violent scenes at pits across the country and clashes with miners who refused to join the strike.
The Thatcher government held firm and the power of the NUM was destroyed, leading years later to a huge programme of pit closures.
Labour retained many of the employment measures when it came to power in 1997, leaving flying pickets, mass picketing and official strikes without ballots confined to the history books.