The government has ruled out any prospect of lifting the ban on secondary industrial action.
Gate Gourmet sacked 670 catering workers at Heathrow
Strikes in support of fellow workers have been illegal since 1980.
But recent wildcat action by Heathrow baggage handlers in support of sacked staff at Gate Gourmet has led to calls for a change in the law.
Despite union calls for a re-think, trade secretary Alan Johnson told Labour's conference the ban would stay.
Mr Johnson pledged there would be no return to the industrial policy of the 1970s.
He said in the party's quest for "full and fulfilling employment we realised that we could not go through the '80s and '90s only to emerge in the '70s".
"Back then, this party supported secondary action and opposed the minimum wage.
"Now it's the other way round - and that's how it needs to stay."
He told the party's annual conference in Brighton that a Labour third term would focus on workers who did not have the protection of trade unions.
Mr Johnson said Britain's trade unions were "a vital part of our democratic process".
"Our third term will also see us focus on those workers who too often do not have the protection of trade unions and who work in a twilight world of exploitation and fear," he said.
The government will also protect workers against age discrimination from next April, he added.
Labour delegates were debating an emergency motion by the Transport and General Workers Union condemning Gate Gourmet management.
The union is calling on the government to lift the ban on secondary action "at least where there is a close connection between those involved".
It also wants simplified strike ballot procedures, protection of strikers from dismissal and a ban on replacing striking workers.