With the paralyzing labor strike now running for a full four weeks, Boeing Co. is taking a harder line with union representatives by filing unfair labor practice charges, saying the other side has bargained in bad faith and undermined its own deal.

The union and the company are each accusing the other of bad-faith bargaining as the strike of over 33,000 employees reaches the end of its first month.

Boeing (NYSE:BA) has filed an unfair labor practice charge against the union representing workers on strike, accusing it of "bad faith bargaining," as the two sides fail to make progress in contract negotiations.