The Department of Trade and Industry today published its review of the Employment Relations Act, which included plans to "fine tune" legislation.
But the DTI said there was no evidence to support changing the central pillars of the act and rejected calls for staff in firms employing fewer than 21 workers to be covered by the law on statutory union recognition.
Calls to change the 40% threshold of workers having to vote in union recognition ballots were also rejected.
The employment relations minister, Alan Johnson, said the law was working well and had helped deliver better working standards. He also claimed it had promoted a new climate of cooperation between workers and employees.
Mr Johnson pointed out that strikes were at an all-time low, while the number of people in work was at a record level.
"With the success of this law, a new culture at work is emerging. Employers and unions are working together," he said.
But Derek Simpson, joint general secretary of the Amicus union, said the review was a "great disappointment", adding: "It will continue the misery of millions of workers who are deprived the pleasure of being represented by trade unions."
Brendan Barber, general secretary elect of the TUC, said the review had been overly influenced by business lobbying.
"While there are some useful advances in this white paper that will make a real difference to people at work, unions will find the government's rejection of many TUC proposals extremely disappointing," he said.
"The government would be unwise to ignore the real anger in unions today.
"Our call for people at work to have a right to be represented by a union when a majority back it, irrespective of the size of the business, is a basic human right."
John Edmonds, the general secretary of the GMB, said: "The government has capitulated to the demands of the CBI and left workers vulnerable by not strengthening union recognition rights or protecting workers while they are on a legal strike.
"This government needs to decide if they are the party for British workers - and therefore stand up for worker's rights - or they are the party for the fat cats and leave British workers susceptible to harassment and mistreatment in the workplace."
John Cridland, deputy director general of the CBI, said employers would breathe a sigh of relief that the government had not "caved in" to union pressure and gone for a wholesale review.
"It would be deeply damaging if ministers tore up an agreement that is currently working well."
The DTI said it would consider modifying aspects of trade union law, including the law on political fund ballots and union elections to lighten the administrative burden.
Reforms that will go ahead include technical changes to the right of workers to be accompanied by a colleague in a disciplinary hearing, and earlier access rights to unions in recognition cases.
The Transport and General Workers Union voiced disappointment that a law allowing workers on legal strike to be sacked after eight weeks will remain.
Roger Lyons, joint general secretary of Amicus, said the announcement was a victory for bad employers, adding: "More than five million workers have had all hope of fairness at work snatched away from them.
"We will continue with our campaign and will not take this lying down."
Bill Morris, general secretary of the TGWU, said: "We are deeply disappointed with the findings of the review. The whole process has been a sham and addresses none of our fundamental concerns, and is a total surrender to the CBI's agenda."
