Rights to protect striking employees from losing their jobs are to take effect from 24 April, the Government has announced.
From that date any employer who dismisses a member of staff for taking part in legal industrial action lasting less than eight weeks will be acting unfairly.
If the action goes on longer dismissal will be unfair unless the employer can prove that "reasonable steps" were taken to resolve the dispute.
This is the first of a series of measures coming in over the next few months designed to strengthen the position of unions.
The rights are being brought in under the Employment Relations Act which reached the statute books in August last year.
Announcing the measure last week, DTI minister Alan Johnson said it will be a "powerful incentive" to both sides to resolve disputes through negotiation.
But David Yeandle, deputy director of employment policy at the Engineering Employers Federation, said it will lead to more strikes, especially as all ballot papers will carry the message that strikers are protected by law.
"If staff know they cannot be dismissed they will be more likely to vote in favour. This is providing a right to strike by the back door," he said.
Don Cuthbert, head of employee relations at Towers Perrin, said few HR departments are geared up to deal with the new right.
In August half of 120 companies questioned by Towers Perrin had not made plans, he said.
"Collective employee relations has not been on the agenda for 20 years. There are not many HR directors in this country who have the skills to deal with it.
"Even those who were around in the 1970s have not handled it as a litigation issue," Cuthbert said.