An army spokeswoman said on Monday that the armed forces took any refusal to obey orders very seriously.
The dismissals come in the face of a threat of dissent in military ranks over Prime Minister Ariel Sharon's plan to remove all illegal Israeli settlements from Gaza as part of disengagement from conflict with the Palestinians.
The six dismissed officers were the highest ranking of a group of 34, all colonists living in the West Bank, who published a letter in a newspaper last week calling any order to implement the Gaza plan as illegal.
The officers had refused to renounce the letter and were dismissed from their command, but retained their ranks, a military spokeswoman said.
The other signatories would be disciplined at a later time.
Colonel Chaim Morad, one of those dismissed, said he thought the measure would not stop other soldiers from threatening to disobey orders to remove settlers.
Colonist leaders have said thousands of soldiers would refuse to remove more than 8000 settlers from Gaza. Some have circulated petitions against the withdrawal for soldiers to sign.
But opinion polls show strong public support in Israel for the plan to quit Gaza, where settlements built on occupied land have come under constant attack in a four-year-old Palestinian uprising.
Soldiers face the daunting task
of removing Israeli settlers
Palestinians have welcomed any Israeli withdrawal from occupied territory but worry that Sharon will use it as leverage to hold on to large settlement blocs in the West Bank in any final peace deal.
Army chief Moshe Yaalon had threatened last week to dismiss the officers behind the letter, published only a day after Sharon had visited an army base to condemn calls to disobey pullout orders as a threat to Israel's existence.
Yaalon reiterated a standing order barring soldiers from signing petitions or participating in political activities, and warned that any soldier doing so would face disciplinary action.
The military last week jailed a soldier for 28 days for urging colleagues to defy orders to remove an illegal settler outpost in the West Bank. The soldier has appealed to the supreme court against the punishment.