World No 7 Ons Jabeur said women players should not have to wait to receive the same prize money as their male counterparts at the Italian Open after tournament organisers announced plans to achieve pay parity by 2025.
Tennis has sought to be a leader in the battle for equality in the last couple of decades with equal prize money offered to men and women at the four Grand Slams.
WTA Tour events, however, still often offer less prize money than those on the separate men's circuit. In the Rome tournament, the total "financial commitment" for the men is $9.51 million while for the women it is $3.5 million.
Italian tennis federation chief Angelo Binaghi said last month the event had started a process that would lead to equal prize money over three years, but Tunisian Jabeur called for immediate change.
"I don't see why we have to wait," Jabeur told the New York Times. "It's really frustrating. It's time for change. It's time for the tournament to do better."
Reuters has contacted the tournament organisers for comment.
Both men's and women's competitors at the tournament - which is one tier below the majors - play best-of-three set matches and the draw for both events features 128 players.
Similar events at Indian Wells, Miami and Madrid offer equal pay for women, although they are listed as mandatory tournaments for players.
Spain's Paula Badosa said she did not understand why there was prize money disparity in Rome, which attracts some of the world's top names.
"I don't know why it's not equal right now," Badosa said. "They don't inform us. They say this is what you get and you have to play."