The Magners League currently features four sides from Wales, four from Ireland and two from Scotland, with Italy hosting its own Super 10 competition.
"At a Magners League board meeting last week... the possibility of developing a relationship with Italian teams was discussed," said Lewis.
"We agreed to positively explore the financial and rugby implications."
Lewis admitted that there is still a long way to go before any decision is finalised but that the WRU at least are not against the idea of expansion.
"As far as we're concerned there's a willingness to look at the possibility. However, we would need to see some firm proposals from Italy. Until we hear something formal from them in terms of a formal proposition then the Celtic Rugby Board isn't really in a position to look at it.
"There are a lot of issues we need to look at - the impact on the fixture list, the commercial impact also and the commercial and financial factors that need to be fully understood.
"The WRU is committed to developing the Magners League to ensure its commercial viability as well as making the rugby even more compelling and engaging for the fans.
"It's important all the Six Nations' standards of rugby increase because that's really how we want the game to go forward. If having teams and playing at a higher level in Italy will enhance the international game then that's something we need to consider."