Birmingham have warned West Ham they will not stand by and watch them snatch two of their key men.
The Hammers have expressed an interest in taking Liam Ridgewell and Sebastian Larsson, with the pair set to be out of contract at the end of the season.
Birmingham believe they have an option to extend those deals by a further 12 months, with both men having a clause in their contract allowing such an agreement to be put in place.
However, new West Ham owners David Sullivan and David Gold, who oversaw the contracts during their days at St Andrews, believe they could take advantage of a perceived loophole.
Sullivan has claimed that the deals may not be permissible under Fifa regulations, meaning the pair could be free to move on in the summer.
Birmingham, though, are adamant that is not the case and have threatened legal action against Sullivan and Gold should they make an approach.
"This man (Sullivan) did the contracts in the first place," said Blues boss Alex McLeish.
"I don't know why they think that they are not recognised by Fifa, but if someone wants to challenge it, it will be four or five years before it is resolved."
Meanwhile, McLeish claims to have received a positive response from the Birmingham board regarding the funds which will be made available to him for strengthening over the summer.
He said: "It was a good meeting. I gave my thoughts that some things needed to be done right now, sowing seeds for players in the summer.
"But I also needed to steal a march on one or two things in order to get the infrastructure right and just to make sure that we've got the oil in the system to get them up and running.
"Do I know how much there will be to spend? We spoke about figures although I am not going to say what they are publicly.
"But they said that, if push came to shove, maybe there would be a wee bit more if we came to them and were asking for a player of certain quality."
He added: "We know that with a small stadium we don't have the revenue of the likes of a Sunderland, Villa have, teams like that.
"Carson (Yeung) has big plans for the club in the future and there could be exciting times ahead in terms of the overall picture.
"But, in the meantime, apart from my long-term vision, the short term is that we get a team that's going to keep us in the Premier League next year."