"The question of the prime minister's leadership, which is symbolized by the Futenma issue, coupled with the question of politics and money involving the top two, is greatly responsible for the drop in public support for the Cabinet," Maehara said.
But some cabinet ministers defended Hatoyama.
Finance minister Naoto Kan, a man some have speculated might become the next prime minister, said he has supported Hatoyama's leadership and "that has not changed".
If Hatoyama does bow to the pressure for him to resign either before or after the upper house election in July, he will be the fourth Japanese prime minister to do so in four years.