Labour's Alan Meale took action after call centre worker Pat Carmody, a union organiser for the Communication Workers' Union, was dismissed from his job at a call centre run by London-based telemarketing company Pell and sales, for speaking to the press without authorisation.
The company reinstated Carmody today after he appealed against the decision.
Tom Dale, also a CWU organiser, urged charities to stay with Pell & Bales and to ask that employees are treated in an "accountable manner".
The firm, whose clients include Oxfam and Christian Aid, does not formally recognise the union. The EDM has so far been signed by 22 MPs.