Japan's opposition Friday made clear that a honeymoon period was over for Prime Minister Yoshihiko Noda's three-month-old cabinet, voting to censure two of his ministers in the parliament's upper house.

The opposition, which controls the upper house, has cooperated with Noda on the passage of a $155 billion (99 billion pounds) budget to fund rebuilding from the March earthquake, tsunami and the nuclear disaster and tax hikes to secure its financing.

But the non-binding censure motion against his defence and consumer affairs ministers is a warning that such cooperation will be hard to come by when Noda will need support for his plan to double the sales tax to 10 percent to cover rising costs of caring for the fast-aging population.

The main opposition Liberal Democratic Party, which lost power to the Democrats in 2009 after half a century of a nearly uninterrupted rule, has made it clear that it wanted to use its ability to block legislation to force Noda to call an early election after the disaster-related laws are passed.

Noda took over in September as Japan's sixth premier in five years facing a multitude of challenges: reining in public debt twice the size of the economy, spearheading the nation's reconstruction efforts and finding new sources of growth in a rapidly-aging society.

Noda has said he was standing by his ministers, but the vote puts him in a bind because keeping them in his cabinet would make it harder to work with the opposition while letting them go could embolden the opposition and weaken his grip on power.

Some analysts suggest Noda could follow the example of his predecessor Naoto Kan to get out of the quandary. When Kan's two ministers were censured in November 2010 he did not dismiss them out of hand, but later replaced them in a cabinet reshuffle.

Switching ministers often cannot be good for Japan. But he might have no option but to let them go in the form of a cabinet reshuffle, said Koichi Nakano, political science professor at Sophia University in Tokyo.

Noda's approval ratings have steadily declined from close to 60 percent after his appointment to less than 40 percent in the past week as government officials' blunders and his embrace of controversial policies such as a U.S.-led free trade pact and tax hikes have taken their toll.

The censure motion against Defence Minister Yasuo Ichikawa was prompted by an offensive comment by a senior defence ministry official over plans to relocate the U.S. Marines' airbase in the southern island of Okinawa.

Ichikawa also came under fire after he told parliament last week he did not know the details of a 1995 Okinawa rape case, in which a 12-year-old girl was assaulted by three U.S. servicemen, stoking anti-U.S. base sentiment on the island.

Consumer Affairs Minister Kenji Yamaoka was censured for his ties with pyramid scheme businesses.

Noda has already suffered an early setback when trade minister Yoshio Hachiro resigned after just eight days in office over comments seen as insensitive about radiation from the tsunami-hit Fukushima nuclear plant.

(Writing by Kiyoshi Takenaka and Tomasz Janowski; Editing by Yoko Nishikawa)