Is it permissible to offer banquets by contractors to employees of the consulting company and the government agency after the handover of projects, especially when the company requests it, and is it permissible to eat from them?

Such banquets fall under the ruling of gifts. Therefore, it is impermissible to request them from contractors, or to accept them from them if they offer them without being requested, unless the employer authorizes their acceptance. This is based on the Prophet’s (peace be upon him) saying: "Gifts to officials are ill-gotten gains (ghulul)."