A $3 billion takeover bid for telecommunications firm Vocus Group has been met with backlash on the market as investors ensured prospective buyer AGL Energy had its worst day on the ASX for close to a year.

The utility company's torrid day saw its share price tumble by 6.55 per cent – or $1.30 – in the early afternoon; a steep decline which was only bettered in July last year when share values dropped 7 per cent.