Yingluck Shinawatra, the caretaker prime minister at the time, waved as she boarded a train from Surin to Si Sa Ket on December 18, 2013, to inspect the route which was reopened after an upgrade.
EC investigators allege that Ms Yingluck, seven ex-cabinet ministers and Pol Gen Adul Saengsingkaew, at that time the national commissioner of police, violated the 2007 constitution by using public funds to campaign for office, the high-placed source probing the case said.
The eight joined her in one or more trips in Bangkok and to other provinces, when Ms Yingluck led the caretaker government, the source explained. The source said that violated Section 181 of the previous constitution, which states that an outgoing cabinet ''shall not exploit the State's resources or manpower in a way that affect the results of the next election.''
The 2007 charter has been replaced by the interim charter written by drafters picked by the junta. Still, the allegations relate to events that occurred while the 2007 constitution was still in effect.
Besides Ms Yingluck and Gen Adul, the others who are facing the same accusations are Charupong Ruangsuwan, Plodprasop Suraswadi, Chatchart Sittipunt, Santi Prompat, Sermsak Pongpanich, Tanusak Lekuthai and Visarn Techathirawat. They were in the caretaker cabinet and some are executive members of the Pheu Thai Party.
The eight joined Ms Yingluck in one or more trips to Chiang Mai, Lampang, Petchabun, Roi Et, Buri Ram, Surin, Si Sa Ket, Kalasin, Loei, Yosothon, Bangkok and Rayong, according to the investigation.
All will be called to defend their actions before the investigative panel, the source said. The board will then decide if the case should be forwarded to the EC for further action.
The EC has to take the case to the Supreme Court's Election Cases Division for ruling. The defendants face a jail term of up to 10 years, a maximum fine of 200,000 baht and a 10-year ban from elections, if found guilty.
In addition, the Pheu Thai Party could be disbanded since some of the accused are executive members.
Ms Yingluck dissolved parliament on December 9 amid street rallies by the People's Democratic Reform Committee (PDRC). A new election was called on February 2, but this was ruled invalid by the Constitutional Court on grounds that it could not be held in a single day.
The trips were arranged when Ms Yingluck was in the caretaker cabinet, which ended with the military coup on May 22.
She spent most of her time in the provinces to avoid continued rallies in Bangkok by the PDRC after the House of Representatives was dissolved.
Ms Yingluck is currently in Europe. She attended the birthday party of her elder brother, Thaksin, in Paris on Saturday and is finding a school for her son in London. She has promised to return to Thailand.
Ms Yingluck already faces a criminal charge on abuse of authority for her failure to stop the government's rice-pledging scheme despite heavy losses and corruption. The National Anti-Corruption Commission charged her and sent the case to the Office of the Attorney-General to indict her in the Supreme Court's Criminal Division for Holders of Political Positions.