When the same survey took place six months earlier, in the same month as the lobby, the proportion who remembered the movement was 35 per cent.
"It shows the volatility of MPs' attitudes," said nfpSynergy co-founder Joe Saxton. "Consistency is the name of the game: you have to keep in the public eye."
Chris Holt, co-ordinator of the Trade Justice Movement, a coalition of 60 organisations representing nine million people, denied her organisation had lost its relevance.
"More MPs were bound to recall us before because it was at the time of a hugely successful campaign," she said. "The engagement we've had with MPs in the months since has been fantastic."
The NSPCC has replaced the Trade Justice Movement in first place in the best-recalled campaign category. Thirty-five percent of MPs questioned remembered the charity.
Macmillan Cancer Relief was named most effective charity for the second-time running. NfpSynergy does the survey twice a year, asking MPs about 20 voluntary organisations that pay to take part.
"Macmillan has a chief executive who is very interested in the political arena and an issue close to many MPs' hearts," said Saxton. "They research their facts well and present ideas that are achievable."
Deafness charity RNID found itself sliding out of the top five in the effectiveness league.
Brian Lamb, the RNID's director of communications, said the fall followed the successful culmination of long-running campaigns. "I'd be surprised if we were high at the moment because we haven't got any major campaigns running," he added.
Saxton commented: "There is always a danger someone else can sneak into your slot if you don't keep up the pressure."
The cross-party survey, which was conducted between 17 January and 14 February, also revealed that hunting featured more prominently in MPs' mail than Iraq.