NEW DELHI (Reuters) - One of Indias biggest corruption scandals in the Congress-led governments six years in power has damaged the partys image, strained ties with a crucial coalition ally and disrupted the passing of reform bills. While the scandal over the granting of 2G licences that prompted the telecoms mini-sters sacking is unlikely to threaten the govts survival, it underscored the fragility of a fickle coalition despite its overwhelming re-election in 2009. At stake is not only the image of Congress, a party that in 1989 lost a general election partly due to a scandal over gun contracts involving close associates of then prime minister Rajiv Gandhi who were accused of taking bribes. The scandal also threatens to drag Prime Minister Man-mohan Singhs second term into further policy limbo. The main opposition party, which has repeatedly blocked progress in parliamentary sessions over the last year, said on Monday it would carry on blocking reform bills. It tainted the entire govern-ment, The Indian Express said of the scandal in an editorial on Tuesday. This is a crucial time ... and we cannot afford to have enormously important matt-ers of governance held up because the ruling coalitions energies are focussed on dousing the fires of impropriety and scandal. The opposition demanded a parliamentary probe after Telecoms Minister Andimuthu Raja resigned on Sunday, after a report from the government auditor said the state may have lost up to $31 billion in revenue in the granting of telecoms licenses in 2007-2008. Earlier media reports had suggested the figure may be as high as $39 billion. Raja is accused of selling the licenses at deliberately low prices to companies, something he denies. The amount lost to the treasury would be roughly equivalent to Indias defence budget. Opposition parties have been calling for his resignation since 2007 but analysts say the crucial support his party gave to the coalition govt prevented Singh from sacking him. The Raja case has followed other graft cases in the last month that saw two senior Congress party officials resign - Suresh Kalmadi, chief organiser of the Delhi Commonwealth Games, and Ashok Chavan, chief minister of Maharashtra state.