Swiss Foreign Minister Micheline Calmy-Rey has been widely criticised for donning a white headscarf to meet Iranian President Mahmoud Ahmadinejad.
Ms Calmy-Rey argued that she was respecting local customs
Well-known for her stand on women's rights, she has provoked headlines such as "Just like a submissive woman".
Socialist MP Maria Roth-Bernasconi said it was irritating that she had angered feminists in Iran.
Ms Calmy-Rey said she was observing protocol. "When you are a guest you respect local customs," she said.
Social Democrat MP Liliane Maury Pasquier accepted that customs had to be observed.
But she was quoted by one newspaper complaining that the minister should have shown solidarity with "the women who fight against wearing the headscarf".
The minister also prompted controversy by signing a multi-billion dollar natural gas deal. The United States had complained that Switzerland was sending the wrong message when Tehran was subject to UN sanctions.
Ms Calmy-Rey insisted the deal between Swiss company EGL and the National Iranian Gas Export company did not violate sanctions.
Swiss daily Le Matin said on Wednesday it was shocked that Switzerland's "icon of a liberated woman" had been transformed into an image of one who was oppressed.
Its tone changed on Thursday, however, by acknowledging that the foreign minister had not really had much choice.
A source told the paper that, without wearing a headscarf, she probably would not have been able to have her meetings with the Iranian leadership.