Singapore may see its 15th by-election with the expulsion of Hougang MP Yaw Shin Leong from the Workers' Party (WP). If it is called by Prime Minister Lee Hsien Loong, it will be the first by-election in exactly 20 years. Eugene Tan, Assistant Professor of law at SMU said that ?It is clear that a by-election has to be called, in this case, because the Parliamentary Election Act states that where there is a vacancy, the Prime Minister would then have to advise the President to issue a writ for election. The law is actually silent on how soon the by-election has to be called, but if we go by convention, then we would see that it will be within a reasonable timeframe, and I think that would be between three and six months."