Gay marriage is not legal in Switzerland, though same-sex couples can enter into a civil partnership after the move was approved in a 2005 referendum.
While many MPs – and, according to a 2015 survey, a majority of the Swiss public – are in favour of marriage equality, hardline conservative MPs have tried to block moves towards it.
Speaking in parliament SVP MP Yves Nidegger said the word marriage was historically linked to the fact that a couple can procreate, reported news agencies.
“To replace it with the word ‘union’ for people who by definition cannot procreate is not only absurd but dangerous,” he said.
But the lower house voted 118 to 71 in favour of launching a parliamentary study on the issue, suggested by the Green Liberal party, which will also examine the idea of extending civil partnerships to heterosexual couples.
The study will consider the impact of marriage equality on Swiss laws concerning tax, social security, adoption and fertility treatment.
Any law changes would have to be passed by the public in a referendum, since they would require changes to the Swiss constitution.
Equal marriage would also have an impact on the naturalization of foreign residents.
Currently, foreign spouses of Swiss citizens are eligible for facilitated naturalization, an easier process than the longer ‘ordinary’ naturalization process. If equal marriage were law, same-sex spouses and heterosexual civil partners could then be eligible for the facilitated system.
The commission is not obliged to suggest legislation over the issue of adoption rights for homosexual couples, said news agencies.
Currently gay people in Switzerland are not allowed to adopt.
Last year parliament took a step towards liberalizing adoption laws by voting in favour of gay people in a civil partnership being able to adopt their partner’s children from a previous relationship.
At the time some MPs opposing the move said they feared it was a ‘salami’ tactic that could lead to legalizing adoption for single gay people and surrogacy. However a campaign to launch a referendum against the law change failed to get the required number of signatures.
Switzerland lags behind other European countries on the issue of gay rights.
The country fell three places in the latest Rainbow Europe ranking by LGBTI advocacy group ILGA-Europe, placing 26 out of 49 countries, far behind the UK, France, Spain and Norway.
Switzerland met just 31 percent of the report’s criteria for equal rights.