Political parties and groups have outlined the changes, including dismantling the Senate, they will pursue to partially amend the charter.

The Progressive Movement said it was looking to spend the next six months gathering at least a million names in a signature campaign to support its own version of the amendment.

The movement plans to seek four key changes: abolishing the Senate; getting rid of the Constitutional Court and independent agencies; cancelling the 20-year national strategy; and wiping out laws and regulations that absolved the 2014 military coup, according to Piyabutr Saengkanokkul, the movement's secretary-general.

Although the law stipulates that at only 50,000 names were needed to mount an amendment bid, Mr Piyabutr said the movement aims to collect a million.

Only a campaign of such magnitude could pressure the Senate and make it see what the people really think of it, he said.

Mr Piyabutr added that even though fixing chapters 1 and 2 is off the radar, "it doesn't mean we won't pay any attention to them."

Chapter 1 contains sections defining Thailand as a single, indivisible kingdom with a democratic regime and the King as head of state. Chapter 2 contains sections that deal with royal prerogatives.

The partial charter changes are being pursued after a recent attempt by many MPs pushing for wholesale amendments was ruled unconstitutional.

Meanwhile, Paiboon Nititawan, deputy leader of the ruling Palang Pracharath Party (PPRP), said the party will submit its amendment draft to parliament today. Its draft is separate from those sponsored by other coalition parties.

He denied the PPRP was leaving the Senate's power untouched.

Mr Paiboon said the party has proposed rewriting Section 270 in the provisional clause of the constitution to hand Senate control over directing the country's reform strategy to the Lower House.

He also noted it was natural that the Senate would resist moves to strip away its power.

The Democrat Party said its amendments include removing the Senate's power to select a prime minister; letting parliament, rather than political parties, nominate prime ministerial candidates; decentralising more power to local authorities; limiting the ability of House panels to summon people to testify; and sorting out the electoral system.