Relatives of Simon Jones, who died at work, will speak
Relatives of those who died in tragedies like the Ladbroke Grove rail crash were also due to lobby MPs over making company directors legally accountable.
Campaigners argue criminal convictions against companies after a worker dies would be much more likely if the law is introduced.
They are also due to call for an increase in the level of fines courts can impose on convicted firms.
She told BBC News Online the most important issue is ensuring company directors become legally responsible for their employees' safety.
"Unless company directors are put in this position they are not actually going to take the issue seriously," she said.
"It's all very well for the government to want to introduce corporate killing, because they don't want to put directors on the spot.
Safety inspectors
"Corporate killing simply means a company will be fined, which will be paid for by shareholders in reduced dividends. Meanwhile the director just walks away."
Following the death of Mrs Jones' son, Euromin was fined for health and safety breaches.
But the company and general manager Richard Martell were found not guilty of manslaughter.
Demands for an increase the number of inspectors for the "under-resourced" Health and Safety Executive are also being raised with MPs.
Others addressing the event include John Monks, general secretary of the TUC, which has organised the event with the Centre for Corporate Accountability (CCA).
Mr Monks said: "Sometimes the human side of these terrible tragedies isn't fully realised, and that is why we [need]...to persuade MPs that action is needed now."
Currently, under corporate manslaughter law, a company can only be convicted if a court establishes a director had a "controlling mind" over the circumstances that led to someone's death.
If the director is found not guilty, the company itself will automatically be cleared as well.
David Bergman, of the CCA said: "Corporate killing will mean a company can be convicted separately.
"This law was a promise from the Labour Party in 1997 - we're still waiting."
A Home Office statement said the Government is "committed to legislation in this area", but parliamentary time has delayed its introduction.
"The current law on manslaughter needs reform," the statement said.
"We have consulted on proposals to reform the law... including a new offence of corporate killing."