Calcutta, April 19 :     In an open challenge to the CPM leadership, transport minister Subhas Chakraborty today dared his party to expel him for praising Trinamul Congress chief Mamata Banerjee publicly at a function organised by the railways last week. The minister's defiance came in the wake of criticism from CPM state secretary Anil Biswas who said his party did not approve of the way Chakraborty glorified the railway minister's contribution to West Bengal. According to Biswas, his party's assessment was Mamata had not done anything so far which could be lauded. When asked about his presence at the function, Chakraborty stood his ground. 'I was officially invited by the railways as the state transport minister. Mamata was there as railway minister and not as Trinamul chief,' he said, emphasising that his presence could not encourage anti-Left forces. 'I have attended such programmes and shared the dais with Nitish Kumar and Ram Vilas Paswan. But no questions were asked then. Any person with a minimum sense would understand the difference between an official programme and a political one,'' he said. Denying that he had praised Mamata, Chakraborty said: 'I have only praised her as a railway minister for increasing allotment of funds for West Bengal projects from 2.5 per cent to over 8 per cent in this year's rail budget.' Chakraborty pointed out that the Left Front government had been demanding early completion of these projects since the past 20 years, but in vain. 'Should we not say a few good words to Mamata for doing justice to our longstanding demands?'' he asked. 'If the CPM leadership feels that I have done harm to the party then why is it not taking action against me?'' But even as the sparks flew, chief minister Jyoti Basu - at a meeting of the CPM's North 24-Parganas unit - denied a report which said he had rebuked the transport minister for praising Mamata. 'It's all rubbish . What you have printed in your papers are nothing but lies,'' Basu told reporters. Biswas, however, played safe when contacted later. 'I have no comments on Chakraborty's statement,'' he said.