Birgitta Ohlsson, foreign affairs spokeswoman for the Liberal Party, one of Sweden's four governing parties, has said Reinfeldt should follow the lead of British Prime Minister Gordon Brown, who has already said he will not attend.
Writing in Saturday's Dagens Nyheter, Ohlsson said that to attend would be a "moral faux-pas".
"Gordon Brown has already set the agenda. I think definitely that the Swedish prime minister should follow his line," she told The Local.
Ohlsson emphasised Zimbabwe's desperate situation:
"I've seen the cruelty against the opposition; I've seen the poverty - around 30 percent of Zimbabwe's population has left the country. 25 percent have HIV," she said.
The Swedish government has yet to make a formal decision on boycotting the summit, although the Liberals' strong opposition will weigh into the decision. Neither Reinfeldt nor Foreign Minister Carl Bildt have said whether Sweden will attend, although Bildt has said Mugabe is "quite simply not welcome," to the summit.
Ohlsson, who visited Zimbabwe last month and who has close contact with the opposition Movement for Democratic Change (MDC), said Sweden has "a great reputation in Zimbabwe." The country's democracy movement will "be very disappointed with us" if Reinfeldt turns up at the EU-Africa summit in Portugal in December, she said.
Portugal, which hosts the EU presidency, and European Commission President Jose Manuel Barroso have responded with dismay to Brown's decision not to attend.
"That would not be fair, nor right, and that would not serve European interests if, because of a political regime or a specific dictator, we could not have a meeting at this level with Africa as a whole," Barroso told Portuguese media this week.
But Ohlsson says that the decision to lift the EU's travel ban on Mugabe so he could attend the summit was "hypocritical".
Ohlsson contrasted the treatment of Mugabe with the EU's attitude to Burma's attendance at the 2004 Europe-Asia summit. On EU insistence a compromise was eventually reached in which Burma only sent a low-level delegation.
"Why can't we have the same attitude to Zimbabwe," Ohlsson asked.
African Union leaders have so far refused to force Zimbabwe to send a low-level delegation, insisting that Mugabe has the right to attend.
China is one factor complicating the EU's attitude to the summit. With the Chinese an increasingly important player in the mineral-rich continent, many EU officials think the summit is necessary to bolster European trade relations with Africa.
Ohlsson said the China issue did complicate matters:
"It is a problem - they are very active on the continent with investment and aid programmes."
"But at least we have the principle of democracy, which the Chinese don't. If we don't stick to our principles, how can we encourage the [Zimbabwean] opposition to stick to theirs."