By Marcin Goettig
WARSAW (Reuters) - A Polish lawmaker quit the ruling Civic Platform party on Tuesday, leaving Prime Minister Donald Tusk's coalition with just a three-seat majority in parliament as it struggles to revive a faltering economy.
John Godson, Poland's first black member of parliament, said he was leaving over disagreements about unspecified social issues - a move which could embolden over members of a conservative faction in the party.
Members of the grouping have already clashed with the more liberal Tusk over in vitro fertilization, civil partnerships for gay couples and other issues.
The government is still likely to be able to get a revision of the budget through parliament in the next few weeks, but the departure of Godson leaves it with a narrow margin for error on other important votes, especially a planned pension reform.
The conservative faction's de facto leader, Jaroslaw Gowin, lost a party leadership election last week to Tusk, but won a surprisingly high 20 percent of votes, signalling growing dissatisfaction with Tusk's leadership.
Civic Platform trails the main right-wing opposition party in opinion polls. A majority of Poles say they are unhappy with Tusk's handling of the economy, which earlier this year came close to the first recession in two decades.
Godson was facing disciplinary action by party managers for abstaining from a vote on a government-backed bill last month.
He said he was also quitting because he was unhappy with the prospect of disciplinary action.
"This is a private decision. And one of the best decisions I have ever made," Godson said.
Godson said he would stay in parliament as an independent and would probably not back a government bill to widen this year's budget deficit.
He said he would also oppose changes to the pension system planned by the government, but would back Civic Platform on other issues.
(Reporting by Marcin Goettig; Editing by Andrew Heavens)