"I call on all to be aware ... and for God to help Lebanon and the Lebanese," said Maronite Patriarch Nasr Allah Sfeir at Sunday mass.
"What happened yesterday regarding the constitution and the presidency is unfamiliar - plotted by night and carried out swiftly by day," he added.
Sfeir was talking about the Lebanese cabinet's approval of a bill to change the constitution, which would allow Lahud to remain in office.
The bill was passed despite protests by the US and EU, who accuse Syria of interfering in Lebanon.
Syria has about 25,000 troops stationed in Lebanon and is considered to be the main power broker in the country.
The US and France are now considering a UN Security Council resolution aimed at curbing Syrian influence in Lebanon's affairs.
"We are discussing with the French a possible resolution"
US State Department official
"We are discussing with the French a possible resolution of the Security Council that would stand up for Lebanon's right to decide its own fate without outside interference," a State Department official said.
The cabinet decision has provoked widespread condemnation in Lebanon.
"To the majority of Lebanese this is a travesty and it is almost farcical," lawyer Mohammad Mattar told Aljazeera.net.
"This amendment was against the popular sentiment in Lebanon... This was at the incitation of the Syrians. It was taken by pressures and coercion," said Mattar, who is also a lecturer in law at Beirut's St Joseph University.
Mattar told Aljazeera.net the decision could cause problems for Syria in the future.
"The Syrians are yet to see the repercussions of what they have done. It's a great violation of international law," he said. "The question of Lebanon could be internationalised."
The cabinet decision is being resisted in Lebanon by a group of opposition figures led by the colourful Druze leader Walid Jumblat.
Jumblatt blasted the measure, saying "freedom and the military are mutually exclusive opposites". Lahud was formerly a commander in the Lebanese Army.
A billboard in Lebanon describes
Lahud as a man who can do it all
Opposition MPs say that a renewed term for Lahud will result in a continuation of the political deadlock in Lebanon. Decision making in recent years has been crippled by continual spats between Lahud and Prime Minister Rafiq Hariri.
Hariri was initially opposed to the move, and there were reports in the Lebanese press that his resignation was imminent. However, after a meeting in Damascus with Syrian President Bashar al-Assad, he changed his position and voted for the plan.
"We think that what they are doing now is not going to serve the interests of Lebanon. Especially considering the president did not manage to solve the problems of Lebanon," opposition MP Butrous Harb told Aljazeera.net.
Harb said he thought the bill would be passed in parliament. He added that the session could be moved forward to Friday in order to pre-empt a Security Council resolution.
He said some MPs who oppose the amendment have received threatening phone calls and faxes.
But Nadim Shihadi, director of the Centre for Lebanese Studies at Oxford University, UK, was still unsure about whether parliament would approve the bill.
"There is still about a week before parliament and anything could happen between now and then. This is just an opening bid," Shihadi told Aljazeera.net.
"There is still about
a week before parliament and anything could happen between
now and then"
Director, Centre for Lebanese Studies at Oxford University, UK
"I am not sure that it will happen… There are many other options such as other candidates."
Despite criticism, Lahud has much support within Lebanon. He counts among his allies the Shia resistance group Hizb Allah.
Information Minister Michel Samaha told Aljazeera.net a change in the constitution was justified.
"This is supported by most of the Lebanese people," he said.
He said the US and France did not have the right to interfere in internal affairs.
"I think this internal issue must not be an issue for the Security Council. They must address the Israeli-Arab issue first."
He added that Lebanon would continue to maintain a close relationship with Syria.