"This is irresponsible of (union) Kommunal," said Peter Jeppsson, CEO of the Swedish Bus and Coach Employers' Association (Bussarbetsgivarna), to the Aftonbladet daily.
"We received an offer from the mediators that we didn't think was perfect, but we extended ourselves and accepted it. Kommunal turned it down and have a significant responsibility when travellers are affected," he added.
The new strike notice on Monday affects bus drivers in Norrköping, Strängnäs, Halmstad, Västerås and Hallstahammar as well as engineering and service staff in Gävle and Östersund.
The expanded strike means that a total of 1,400 staff were involved as of midnight on Sunday.
Trade unions are demanding that scheduling is reviewed to prevent the current situation of up to 13-hour days with few breaks.
Further demands include a salary increase of 1,760 kronor ($263) per month over three years and an employment guarantee when a new operator takes over bus services.
Employers and unions now have a week to reach a deal or face the prospect of a further expansion of the strike on Saturday June 29th that will affect, among other services, airport coaches.