The oath of loyalty to the Queen should be re-examined if it meant Sinn Fein would take their Commons seats, the Conservative NI spokesman has said.
Sinn Fein has five seats at Westminster
David Lidington made the comments before a debate on proposals to restore Sinn Fein's Westminster allowances.
Mr Lidington said a general commitment to uphold the law and democratic politics could be considered as an alternative to the compulsory oath.
Sinn Fein has said it will not take its Commons' seats under any circumstances.
"If Sinn Fein said it was the wording of the oath that was the sole obstacle, then I think that it's something any government would have to be willing to re-examine," Mr Lidington said.
"But at the moment Sinn Fein are taking a very firm line and saying it's not the wording of the oath, it goes far beyond that."
On Wednesday, Martin McGuinness, Sinn Fein MP for Mid Ulster, said he did not envisage any circumstances ever in the future in which any Sinn Fein MP would take their seat.
Mr McGuinness said, while it was quite legitimate for Sinn Fein elected representatives to go to Westminster to engage with other parties, they did not recognise the right of the British Parliament to rule over any part of Ireland.
The Commons allowances are worth about £500,000 to Sinn Fein's five MPs.
Following a General Election, all MPs and peers must take an oath of allegiance to the monarch before they can take part in the work of Parliament.
The debate on Sinn Fein's allowances is expected to take most of Wednesday afternoon in the Commons.
COMMONS OATH OF ALLEGIANCE
I swear by Almighty God [or, I do solemnly and sincerely affirm] that I shall be faithful and bear true allegiance to Her Majesty Queen Elizabeth, her heirs and successors according to law [So help me God]
They were withdrawn last year after allegations of IRA involvement in the Northern Bank robbery.
The government wants to restore the allowances in recognition of the IRA's disarmament initiative last year.
It is also proposing to pay Sinn Fein £80,000 a year assistance for the party's representative business.
Sinn Fein's Conor Murphy said the party was entitled to the money.
"The allowances that are afforded to people isn't dependent on anyone sitting at Westminster," the Newry and Armagh MP said.
BBC Northern Ireland political editor Mark Devenport said that both payments would be backdated to November last year, if approved by MPs.
"Some MPs have objected to the additional financial assistance, arguing that a new kind of allowance is being specifically created for Sinn Fein," he said.