Republican Senator John Eichelberger has announced he intends to introduce a bill to amend the Pennsylvania Constitution to ban gay marriage.
Currently, Pennsylvania law defines marriage as being between a man and a woman. However, a judge could overturn this law.
Eichelberger and other gay marriage opponents say writing the law into the constitution will ensure gay marriages cannot be passed into law.
To amend the constitution, the proposal requires approval from both the House and Senate in two consecutive two-year sessions. The measure would then go to voters in a state referendum.
Two similar measures have failed in recent years.
Pennsylvania has one of the oldest populations in the country, with older citizens still showing high disapproval of gay marriage. It is also heavily Catholic.
However, it has been tipped as one of the states which will recognise gay marriage soon.
Nate Silver, one of the nation’s top analysts of political data, recently created a map predicting when all 50 states would legalise gay marriage.
Based on factors such as religious power and voter demographics, he predicted that Pennsylvania will legalise gay marriage in 2012.
Currently, Iowa, Connecticut, Massachuesetts, Vermont and Maine allow gay marriage. New Hampshire will be next, once amendments are made to a current bill.