The planned price hike is due to take effect from Sunday.
The petition was filed Thursday by Foundation for Consumers secretary-general Saree Aongsomwang, Confederation of Consumer Organisations chairwoman Bunyuen Siritha and Bangkok senator Rosana Tositrakul.
The group has filed a lawsuit against Prime Minister Yingluck Shinawatra, the cabinet and the Energy Policy Committee, asking the court to repeal the cabinet's approval of the hike.
The cabinet on Aug 13 approved the plan to increase the LPG price by 50 satang/kg every month from Sept 1 until the price reaches 24.82 baht/kg.
The government has said the LPG price float is aimed at reducing fuel subsidies burdening the state-owned Oil Fund.
Since 2008, the LPG price has been subsidised by the fund for a total cost of 100 billion baht. Without the float, the amount is estimated to exceed 200 billion baht by 2015.
In the petition, the group asked the court to order the government to maintain the LPG price for household use at 18.13 baht/kg until the court rules on the case.
Ms Saree said the government's move to increase the LPG price is unlawful because it failed to hear opinions from the Consumer Protection Board, which was formed under Section 61 of the charter.
Ms Saree recommended other measures be used to reduce financial burdens instead of the LPG price float.
Alternative measures include a government order for the petrochemical sector to contribute to the Oil Fund at 12.55 baht/kg of gas in line with other industries, which should add 30 billion baht to the fund next year.
The petrochemical sector currently contributes only 1 baht/kg to the fund, she said.
The fund's losses from subsidising oil prices presently stand at 4.6 billion baht.
Ms Saree also recommended the gas transmission pipeline tariff be lowered to reflect the actual cost and the gas prices for every purchaser be set at the same rate.
Ms Rosana said the Energy Policy Committee was not authorised to assign priority to the household and petrochemical sectors for use of gas.
The cabinet's approval of such a decision is deemed illegal, she added.
Meanwhile, Lampang Ceramic Association chief Thanachot Wanawat said Thursday that ceramic manufacturers in the provinces wanted the Yingluck administration to help solve soaring production costs arising from government policies, including the LPG price hike and the 300-baht daily minimum wage.
The LPG price float from Sunday would push up production costs by 20-30% for small- and medium-sized operators, he said.
Mr Thanachot said five ceramic SMEs in his association have shut down operations as a result of rising gas and labour costs. Up to 20 other operators are expected to go under soon, he said.
The association has lodged its demands with the government. They include setting up a ceramic cooperative, a 1.5-billion-baht credit line carrying 3% interest, and a 600-million-baht budget for the construction of a central ceramic furnace, Mr Thanachot said.
The government has not responded to the demands yet, he said.